Holographic optical combiners for head-up displays

ABSTRACT

Optical Combiners are provided for use in Head-Up Displays. The Combiners have a refractive index modulation greater than approximately 0.001.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of Ser. No. 07/144,840,Process of Forming Reflection Holograms in Photopolymerizable Layers,filed Jan. 15, 1988 now abandoned.

FIELD OF THE INVENTION

This invention relates to Head-Up Displays (HUDs) and, moreparticularly, to improved holographic optical combiners that employ aphotopolymer film imaged to contain a reflection hologram that functionsby diffracting light.

DISCUSSION OF THE BACKGROUND AND PRIOR ART

HUDs are used to display information on the windshield of a vehicle,such as an aircraft or automobile, in order that the person controllingthe vehicle has ready access to the information without the need todivert attention to an instrument panel. The desired information isoptically projected onto the windshield, where it is reflected into theviewer's line of sight. In other applications, the information may beprojected onto a transparent screen between the operator and thewindshield, or onto a visor worn by the operator (e.g., a pilot), andthen reflected to the operator. Thus, the operator has immediate accessto the information while continuing to view the path of the vehicle.

The element used to reflect the information to the operator is commonlyreferred to as an "Optical Combiner" or, more simply, as a Combiner.

To be effective, the Combiner must have several properties. First, itmust selectively reflect only a narrow band of light and be transparentto other wavelengths. Thus, information projected onto the windshieldwill be reflected to the operator while other wavelengths pass throughthe Combiner, enabling the operator to view the path of the vehicle.Secondly, it is desirable that the Combiner have a high reflectionefficiency for the light band used to display information in order thatthe information can be easily observed.

Combiners are generally made by recording a refractive index image in atransparent film element, using the technique for forming reflectionholograms generally described in U.S. Pat. No. 3,532,406 ("Hartman").The imaged film is then laminated into or onto the windshield in HUDapplications. In the method described by Hartman, also known as the"off-axis" method of forming reflection holograms, a beam of coherentlight is split into two beams that are projected onto opposite sides ofthe film element. If the two beams enter the film element essentiallynormal to its plane, interference fringes will be formed within theelement that are substantially parallel to its plane. Alternatively, ifthe two beams enter the element at different angles, the interferencefringes will be formed at an angle to that of the plane (i.e., thefringes will be "slanted"). In either case the interference fringes areformed from a modulation in refractive index and thus diffract lighthaving a wavelength determined by spacing of the fringes.

Dichromated gelatin is currently the material of choice for makingCombiners due to its high diffraction efficiency, wide bandwidthresponse, and high values of refractive index modulation (i.e.,dichromated gelatin exhibits low "background noise"). However,dichromated gelatin has poor shelf life and requires wet processingafter the material has been imaged. Due to its poor shelf life, thematerial must be freshly prepared shortly before imaging or prehardenedgelatin must be used, which reduces image efficiency. Wet processingintroduces an additional step in preparation of the holographicCombiner, and causes dimensional changes in the material as it swells,then shrinks, during processing. These dimensional changes affectspacing of the interference fringes. Thus, it is difficult and timeconsuming to reproducibly make high quality reflection holograms withdichromated gelatin.

Substantially solid, photopolymer films have heretofore been proposedfor use in making holograms. U.S. Pat. No. 3,658,526 to Haugh, forinstance, discloses preparation of stable, high resolution hologramsfrom solid, photopolymerizable films by a single step process wherein apermanent refractive index image is obtained by a single exposure to acoherent light source bearing holographic information. The holographicimage thus formed is not destroyed by subsequent uniform exposure tolight, but rather is fixed or enhanced.

Despite the many advantages of the materials proposed by Haugh, theyoffer only limited viewing response to visible radiation and applicationhas been limited to transmission holograms where the holographic imageis viewed by diffraction patterns created in light transmitted throughthe imaged material. Moreover, the materials disclosed in Haugh havelittle or no reflection efficiency when the material is imaged to form areflection hologram. Thus, there continues to be a need for improvedmaterials for use in preparing reflection holograms in general, and aneed for improved Optical Combiners offering the processing advantagesof the photosensitive elements proposed by Haugh.

SUMMARY OF THE INVENTION

It has now been found that certain photopolymer films, when imaged withcoherent light to form a reflection holographic mirror, will have arefractive index modulation greater than 0.001 and are particularlysuited for use as Optical Combiners in HUDs. Accordingly, the presentinvention provides a Combiner comprising a transparent substrate thatbears a transparent polymeric film containing a mirror formed by areflection hologram, said film having a refractive index modulationgreater than approximately 0.001 and being formed by exposing tocoherent light a composition consisting essentially of:

(a) approximately 25 to 90% of a polymeric binder selected from thegroup consisting of polyvinyl acetate, polyvinyl butyral, polyvinylacetal, polyvinyl formal, interpolymers containing major segmentsthereof, and mixtures thereof;

(b) approximately 5 to 60% of an ethylenically unsaturated monomerselected from the group consisting of carbazole containing monomers anda liquid monomer containing one or more phenyl, biphenyl, phenoxy,naphthyl, naphthyloxy, heteroaromatic group containing up to threearomatic rings, chlorine and bromine;

(c) approximately 0 to 25% of a plasticizer; and

(d) approximately 0.1 to 10% of a photoinitiator system activatable byactinic radiation wherein said percentages are weight percentages basedon total film weight. Particularly useful are Combiners having areflection efficiency of at least 15%.

It also has been found, surprisingly, that reflection efficiency of theCombiner is improved if the film is treated with a liquid enhancingagent, or is heated to a temperature of at least 50° C., after the filmis imaged to form the mirror.

In another embodiment, the present invention provides a method forforming a Combiner by the steps of:

(a) mounting a transparent support onto one side of a transparentpolymeric film having a refractive index modulation of at least 0.001when imaged, said film consisting essentially of:

(1) approximately 25 to 90% of a polymeric binder selected from thegroup consisting of polyvinyl acetate, polyvinyl butyral, polyvinylacetal, polyvinyl formal, interpolymers containing major segmentsthereof, and mixtures thereof;

(2) approximately 5 to 60% of an ethylenically unsaturated monomerselected from the group consisting of carbazole containing monomers anda liquid monomer containing one or more phenyl, biphenyl, phenoxy,naphthyl, naphthyloxy, heteroaromatic group containing up to threearomatic rings, chlorine and bromine;

(3) approximately 0 to 25% of a plasticizer; and

(4) approximately 0.1 to 10% of a photoinitiator system activatable byactinic radiation wherein said percentages are weight percentages basedon total film weight;

(b) exposing the mounted film to coherent light in a manner that forms areflection hologram in said film; and

(c) laminating the imaged film to a permanent transparent substrate.

The transparent support conveniently is a flexible film, such aspolyethylene terephthalate, which may be removed after the film islaminated to its permanent substrate, such as glass or a transparentplastic substrate. Generally the film will be imaged with coherent lightprior to being laminated to the permanent substrate, but it may beimaged after lamination if so desired. Lamination is generallyaccomplished through the application of heat and pressure; transparentadhesives also may be used to achieve permanent bonding of the film tothe substrate, if so desired. The transparent support generally isremoved after the lamination, but may be left in place as a protectivecovering in some applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an off-axis method of forming a reflectionholographic mirror.

FIG. 2 illustrates a Head-Up Display System.

DETAILED DESCRIPTION OF THE INVENTION

In practicing the invention, the photosensitive composition describedhereinafter is first cast or laminated to a transparent support thatprovides structural integrity for the composition (referred to herein asa film) as it is processed to form a Combiner. Since the photosensitivefilm typically will be only 1 to 100 micrometers in thickness, thesupport is necessary to prevent film rupture or any stretching duringprocessing that would affect spacing of the interference fringes createdin the film that form the holographic image.

The transparent support must have sufficient optical quality that itdoes not unduly absorb or scatter coherent light passing through itduring formation of the holographic mirror. Also, the support must besufficiently flexible that it will not separate from the film as thefilm is brought into contact with its permanent mounting surface, suchas a curved substrate (e.g., a windshield or helmet visor). Less, ifany, flexibility will be needed if the permanent mounting surface isplanar, such as a sheet of glass. Exemplary transparent supports thatmay be selected to advantage include polyethylene terephthalate film,polymethyl methacrylate, polycarbonate, and cellulose triacetate.

POLYMERIC FILM

The polymeric film is substantially solid, transparent, and sufficientlyflexible that it can be brought into intimate contact with a surface(e.g., a windshield, helmet visor, or glass sheet) to which it will bemounted. Components of the film include a binder, an ethylenicallyunsaturated monomer, optionally a plasticizer, and a photoinitiatorsystem. Upon exposure to coherent light as described hereinafter, themonomer polymerizes to form higher molecular weight polymers having adifferent refractive index and rheological properties than unexposedarea of the film. Although the film is substantially solid, componentsinterdiffuse before, during, and after the exposure to coherent lightuntil they are fixed by a final uniform exposure to actinic radiation orby thermal treatment at elevated temperatures. The film typically has athickness of approximately 1 to 100 micrometers. Thinner films generallywill not achieve useful reflection efficiencies. The film reflectsradiation (e.g., light) having a spectral and angular bandwidthdetermined by the thickness and refractive index modulation of the film.Thus, the hologram thickness is matched to the optical requirements ofthe film and the optical system; i.e., the bandwidth of light that willbe used to illuminate the hologram in use (i.e., the display source). Ingeneral, relatively thick films will be selected for narrow bandwidthapplications, and relatively thin films will be selected for broadbandwidth applications.

BINDER

The binder is the most significant component affecting physicalproperties of the substantially solid photopolymerizable film. Thebinder also serves as a matrix for the monomer and photoinitiator systemprior to exposure, provides the base line refractive index, and afterexposure contributes to the physical and refractive indexcharacteristics needed to form the reflection hologram. Cohesion,adhesion, flexibility, miscibility and tensil strength, in addition toindex of refraction, are some of the properties to be considered inselecting the binder for a specific application. Binders that may beselected to advantage in practicing the invention include polyvinylacetate, polyvinyl butyral, polyvinyl acetal, polyvinyl formal,interpolymers containing major segments of these polymers, and mixturesthereof. Fluorine containing binders, such as copolymers of vinylacetate and tetrafluoroethylene, may be selected to advantage when it isdesired to achieve a high refractive index modulation, such as 0.06 to0.07.

MONOMERS

The film will contain at least one ethylenically unsaturated monomerthat is capable of free radical addition polymerization to produce acrosslinked polymeric material having a refractive index substantiallydifferent from that of the binder. The monomer usually will contain theethylenically unsaturated groups in the terminal position. A liquidmonomer generally will be selected, but solid monomers can be used toadvantage, either individually or in combination with a liquid monomer,provided that the solid monomer is capable of interdiffusing in thesubstantially solid film composition and of reacting to form a polymeror copolymer having a refractive index shifted from that of the unimagedcomposition.

Ethylenically unsaturated monomers useful in the practice of thisinvention are solid ethylenically unsaturated carbazole monomers (e.g.,N-vinyl carbazole) and/or a liquid, ethylenically unsaturated compoundcapable of addition polymerization and having a boiling point above 100°C. The monomer contains either a phenyl, phenoxy, naphthyl, naphthyloxy,heteroaromatic group containing up to three aromatic rings, chlorine orbromine. The monomer contains at least one such moiety and may containtwo or more of the same or different moieties of the group, provided themonomer remains liquid. Contemplated as equivalent to the groups aresubstituted groups where the substitution may be lower alkyl, alkoxy,hydroxy, phenyl, carboxy, carbonyl, amino, amido, imido or combinationsthereof provided the monomer remains liquid and diffusable in thephotopolymerizable layer. Suitable monomers which can be used as thesole monomer or in combination with liquid monomers of this type includebut are not limited to styrene, 2chlorostyrene, 2-bromostyrene,methoxystyrene, phenyl acrylate, ρ-chlorophenyl acrylate, 2-phenylethylacrylate, 2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate, phenolethoxylate monoacrylate, 2-(ρ-chlorophenoxy)ethyl acrylate, benzylacrylate, 2-(1-naphthyloxy)ethyl acrylate,2,2-di(ρ-hydroxyphenyl)propane diacrylate or dimethacrylate,2,2-di-(ρ-hydroxyphenyl)propane dimethacrylate,

polyoxyethyl-2,2-di-(ρ-hydroxyphenyl)propane dimethacrylate,di-(3-methacryloxy-2-hydroxypropyl) ether of bisphenol-A,di-(2-methacryloxyethyl) ether of bisphenol-A,di(3-acryloxy-2-hydroxypropyl) ether of bisphenol-A, di(2-acryloxyethyl)ether of bisphenol-A, ethoxylated bisphenol-A diacrylate,di(3-methacryloxy-2-hydroxypropyl) ether of tetrachloro-bisphenol-A,di-(2-methacryloxyethyl) ether of tetrachloro-bisphenol-A,di-(3-methacryloxy-2-hydroxypropyl) ether of tetrabromo-bisphenol-A,di-(2-methacryloxyethyl) ether of tetrabromo-bisphenol-A,di-(3-methacryloxy-2hydroxypropyl) ether of diphenolic acid,1,4benzenediol dimethacrylate 1,4-diisopropenyl benzene,1,3,5-triisopropenyl benzene, hydroquinone methyl methacrylate, and2-[B-(N-carbazoyl)propionyloxy]ethyl acrylate.

Preferred liquid monomers for use in this invention are 2-phenoxyethylacrylate, 2-phenoxyethyl methacrylate, phenol ethoxylate monoacrylate,2-(ρ-chlorophenoxy)ethyl acrylate, ρ-chlorophenyl acrylate, phenylacrylate, 2-phenylethyl acrylate, di(2acryloxyethyl)ether ofbisphenol-A, ethoxylated bisphenol-A diacrylate, 2-(1-naphthyloxy)ethylacrylate, ortho-biphenyl methacrylate, and orthobiphenyl acrylate.

Ethylenically unsaturated carbazole monomers having ethylenicsubstitution on the nitrogen atom of the carbazole moiety typically aresolids. Suitable monomers of this type include N-vinyl carbazole and3,6-dibromo-9-vinyl carbazole. Of these N-vinyl carbazole is preferred.A particularly preferred ethylenically unsaturated monomer comprisesN-vinyl carbazole used in combination with the above preferred liquidmonomers and, in particular, with 2-phenoxyethyl acrylate, phenolethoxylate monoacrylate, ethoxylated bisphenol-A diacrylate, or mixturesthereof.

While most monomers useful in this invention are liquids, they may beused in admixture with one or more ethylenically unsaturated solidmonomers such as the ethylenically unsaturated carbazole monomersdisclosed in Journal of Polymer Science: Polymer Chemistry Edition. Vol.18, pp. 9-18 (1979) by H. Kamogawa et al.; 2-naphthyl acrylate;pentachlorophenyl acrylate; 2,4,6-tribromophenyl acrylate; bisphenol-Adiacrylate; 2-(2-naphthyloxy)ethyl acrylate; N-phenyl maleimide;ρ-biphenyl methacrylate; 2-vinylnaphthalene; 2-naphthyl methacrylate;N-phenyl methacrylamide; and t-butylphenyl methacrylate.

In the embodiment of this invention where crosslinking is desirable,e.g., during thermal enhancement and curing, up to about 5 weight percent of at least one multifunctional monomer containing two or moreterminal ethylenically unsaturated groups typically is incorporated intothe photopolymerizable layer. Suitable such multifunctional monomers arethe acrylic adducts of bisphenol-A ethers identified above and acrylateand methacrylate esters such as: 1,5-pentanediol diacrylate, ethyleneglycol diacrylate, 1,4-butanediol diacrylate, diethylene glycoldiacrylate, hexamethylene glycol diacrylate, 1,3propanediol diacrylate,decamethylene glycol diacrylate, decamethylene glycol dimethacrylate,1,4cyclohexanediol diacrylate, 2,2-dimethylolpropane diacrylate,glycerol diacrylate, tripropylene glycol diacrylate, glyceroltriacrylate, trimethylolpropane triacrylate, pentaerythritoltriacrylate, polyoxyethylated trimethylolpropane triacrylate andtrimethacrylate and similar compounds as disclosed in U.S. Pat. No.3,380,831, pentaerythritol tetraacrylate, triethylene glycol diacrylate,triethylene glycol dimethacrylate, polyoxypropyltrimethylol propanetriacrylate (462), ethylene glycol dimethacrylate, butylene glycoldimethacrylate, 1,3-propanediol dimethacrylate, 1,2,4-butanetrioltrimethacrylate, 2,2,4-trimethyl-l,3-pentanediol dimethacrylate,pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate,trimethylolpropane trimethacrylate, 1,5-pentanediol dimethacrylate, anddiallyl fumarate.

Preferred multifunctional monomers include a diacrylate ordimethacrylate of a bisphenol-A epoxy adduct such as di(2-acryloxyethyl)ether of bisphenol-A, ethoxylated bisphenol-A diacrylate,di(3-acryloxy-2-hydroxyphenyl) ether of bisphenol-A, anddi(2-acryloxyethyl) ether of tetrabromo-bisphenol-A.

PLASTICIZERS

The polymeric film may contain a plasticizer to modify adhesion,flexibility, hardness, and other mechanical properties of the film inconventional fashion. Suitable plasticizers include triethylene glycol,triethylene glycol diacetate, triethylene glycol dipropionate,triethylene glycol dicaprylate, triethylene glycol dimethyl ether,triethylene glycol bis(2-ethylhexanoate), tetraethylene glycoldiheptanoate, poly(ethylene glycol), poly(ethylene glycol) methyl ether,isopropylnaphthalene, diisopropylnaphthalene, poly(propylene glycol),glyceryl tributyrate, diethyl adipate, diethyl sebacate, dibutylsuberate, tributyl phosphate, tris(2-ethylhexyl) phosphate, Brij® 30[C₁₂ H₂₅ (OCH₂ CH₂)₄ OH], and Brij® 35 [C₁₂ H₂₅ (OCH₂ CH₂)₂₀ OH].Particularly preferred plasticizers are triethylene glycol dicaprylateand tetraethylene glycol diheptanoate. Similarly, triethylene glycoldicaprylate and tetraethylene glycol diheptanoate are preferred for usewith solid monomers, such as carbazole monomers, in the absence of anysecond liquid monomers.

PHOTOINITIATOR SYSTEMS

The photoinitiator system has one or more compounds that directlyfurnish free-radicals when activated by actinic radiation. By "actinicradiation" is meant radiation from a light source, such as a laser, thatcauses the compound(s) to produce free-radicals to initiatepolymerization of the monomer. The system also may contain a sensitizerthat is activated by the actinic radiation, causing the compound tofurnish the free-radicals. Useful photoinitiator systems typically willcontain a sensitizer that extends spectral response into the nearultraviolet, visible, and/or near infrared spectral regions.

A large number of free-radical generating compounds, including redoxsystems such as Rose Bengal/2-dibutylaminoethanol, may be selected toadvantage. Photoreducible dyes and reducing agents such as thosedisclosed in U.S. Pat. Nos.: 2,850,445; 2,875,047; 3,097,096; 3,074,974;3,097,097; 3,145,104; and 3,579,339; as well as dyes of the phenazine,oxazine, and quinone classes; ketones, quinones;2,4,5-triphenylimidazolyl dimers with hydrogen donors, and mixturesthereof as described in U.S. Pat. Nos.: 3,427,161; 3,479,185; 3,549,367;4,311,783; 4,622,286; and 3,784,557 can be used as initiators. Otherinitiators are dye-borate complexes disclosed in U.S. Pat. No.4,772,541; and trichloromethyl triazines disclosed in U.S. Pat. Nos.4,772,534 and 4,774,163. A useful discussion of dye sensitizedphotopolymerization can be found in "Dye Sensitized Photopolymerization"by D. F. Eaton in Adv. in Photochemistry. Vol. 13, D. H. Volman, G. S.Hammond, and K. Gollinick, eds., Wiley-Interscience, New York, 1986, pp.427-487. Similarly, the cyclohexadienone compounds of U.S. Pat. No.4,341,860 are useful as initiators.

Preferred photoinitiators include CDM-HABI, i.e.,2-(o-chlorophenyl)-4,5-bis(m-methoxyphenyl)-imidazole dimer; o-Cl-HABI,i.e., 1,1'-biimidazole, 2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenyl-;and TCTM-HABI, i.e., lH-imidazole,2,5-bis(o-chlorophenyl)-4-[3,4-dimethoxyphenyl]-, dimer, each of whichis typically used with a hydrogen donor.

Sensitizers useful with photoinitiators include methylene blue and thosedisclosed in U.S. Pat. Nos. 3,554,753; 3,563,750; 3,563,751; 3,647,467;3,652,275; 4,162,162; 4,268,667; 4,351,893; 4,454,218: 4,535,052; and4,565,769. A preferred group of sensitizers include thebis(p-dialkylaminobenzylidene) ketones disclosed in Baum et al., U.S.Pat. No. 3,652,275, and the arylyidene aryl ketones disclosed in Dueber,U.S. Pat. No. 4,162,162.

Particularly preferred sensitizers include the following: DBC, i.e.,cyclopentanone; 2,5-bis-{[4-(diethylamino)-2-methylphenyl]-methylene};DEAW, i.e., cyclopentanone, 2,5-bis{[4-(diethylamino)-phenyl]methylene};dimethoxy-JDI, i.e., 1H-inden-l-one,2,3-dihydro-5,6-dimethoxy-2-[(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizin-9-yl) methylene]-; and JAW, i.e.,cyclopentanone,2,5-bis[(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizing-9-yl)methylene];which have the following structures respectively: ##STR1## Otherparticularly useful sensitizers are cyclopentanone,2,5-bis[2-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene) ethylidene],CAS 27713-85-5; and cyclopentanone,2,5-bis[2-(l-ethylnaphtho[1,2-d]thiazol-2(1H)-ylidene)ethylidene], CAS27714-25-6.

OPTIONAL COMPONENTS

Other components conventionally added to photopolymer compositions canalso be present to modify the physical properties of the film. Suchcomponents include: optical brighteners, ultraviolet radiation absorbingmaterial, thermal stabilizers, hydrogen donors, adhesion modifiers,coating aids, and release agents.

Useful optical brighteners include those disclosed in Held U.S. Pat. No.3,854,950. A representative optical brightener is7-(4'-chloro-6'-diethylamino-1',3',5'-triazine-4'-yl) amino 3-phenylcoumarin. Ultraviolet radiation absorbing materials useful in theinvention are also disclosed in Held U.S. Pat. No. 3,854,950.

Useful thermal stabilizers include: hydroquinone, phenidone,p-methoxyphenol, alkyl and aryl-substituted hydroquinones and quinones,tert-butyl catechol, pyrogallol, copper resinate, naphthylamines,betanaphthol, cuprous chloride, 2,6-di-tert-butyl p-cresol,phenothiazine, pyridine, nitrobenzene, dinitrobenzene, p-toluquinone andchloranil. The dinitroso dimers described in Pazos U.S. Pat. No.4,168,982, also may be selected. Normally a thermal polymerizationinhibitor will be present to increase stability in the storage of thephotopolymerizable composition.

Hydrogen donor compounds that function as chain transfer agents in thephotopolymer compositions include: 2-mercaptobenzoxazole,2-mercaptobenzothiazole, 4-methyl-4H-l,2,4-triazole-3-thiol, etc.; aswell as various types of compounds, e.g., (a) ethers, (b) esters, (c)alcohols, (d) compounds containing allylic or benzylic hydrogen, (e)acetals, (f) aldehydes, and (g) amides disclosed in column 12, lines 18to 58 of MacLachlan U.S. Pat. No. 3,390,996. Suitable hydrogen donorcompounds for use in systems containing both biimidazole type initiatorand N-vinyl carbazole are 5-chloro-2-mercaptobenzothiazole;2-mercaptobenzothiazole; 1H-1,2,4-triazole-3-thiol;6-ethoxy-2mercaptobenzothiazole; 4-methyl-4H-1,2,4-triazole-3-thiol;1-dodecanethiol; and mixtures thereof.

FILM COMPOSITION

Proportions of ingredients in the photopolymer composition generallywill be within the following percentage ranges, based on total weight ofthe composition: binder, 25 to 90%, preferably 45 to 75%; monomer, 5 to60%, preferably 15 to 50%; plasticizer, 0 to 25%, preferably 0 to 15%;photoinitiator system, 0.1 to 10%, preferably 1 to 7%; and optionalingredients, 0 to 5%, typically 1 to 4%. If the amount of binder isbelow approximately 25%, or the amount of monomer exceeds approximately60%, the composition has insufficient viscosity to form a solid film.The presence of binder is held within approximately 90% sinceperformance is unduly lost at higher levels of addition, and resultingfilms have diminished values of refractive index modulation. Likewise,levels of monomer used will be at least approximately 5% since lowerquantities will not produce films having practical values of refractiveindex modulation.

The composition may be directly coated onto the transparent supportdescribed hereinbefore, or may be cast as a film that is then laminatedto the transparent support by conventional methods. In either case thetransparent support generally provides only temporary dimensionalstability for the photopolymer film prior to mounting on its permanentsubstrate, and thus the support is releasable from the film. For someapplications, however, it may be desired to retain the support as apermanent overcoat or protective layer for the photopolymer film, inwhich case the support and photopolymer film may be permanently bonded.The other side of the supported photopolymer film may have a temporaryprotective cover sheet, such as a polyethylene or polypropylene film,releasably adhered thereto. Conventional intermediate layers or coatingsmay be used to facilitate the adhesive and/or release characteristicsdesired for a particular application.

EXPOSURE OF THE FILMS

Referring to FIG. 1, holographic mirrors may be formed, using the"off-axis" technique, by exposing the films to the intersection of twocounter propagating laser beams. The laser (10) produces a laser beam(12) which is controlled by a shutter (14). The laser beam (12) isdirected by a mirror (16) into a beam splitter (18) wherein the beam isdivided into two equal beam segments (20). Each beam segment (20) passesthrough a microscope objective (22), pinhole (spacial filter) (24), andcollimating lens (26) to produce an expanded, collimated beam (28). Eachexpanded, collimated beam (28)- is reflected by a mirror (36) toconverge in the photopolymerizable layer (32). The photopolymerizablelayer (32) is mounted on a glass plate (34) and protected by apolyethylene terephthalate film support (30).

Interference fringes are created within the photopolymerizable layer bydirecting the two beams into the layer at different angles. In theembodiment shown in FIG. 1, this is achieved by simply tilting the glassplate to an angle of 5° to 70° from the line perpendicular to the axisof the two beams. The interference fringes thereby created in thephotopolymer are slanted (i.e., the fringes are at an angle to the filmplane). The fringes function as a mirror for light having a wavelengthsimilar to that used to form the fringes, and impacting the film at thesame angle that was used to form the fringes.

Alternatively, one may use an "on-axis" technique for imaging the film.In this case a coherent beam of light, such as a collimated 488 nmargon-ion laser beam, is projected onto one surface of the film,typically at an angle up to 70° from the normal to the film plane. Thecollimated beam in part functions as a "reference beam", while a portionis transmitted through the layer and reflected back by a mirror mountedbehind the film, thereby functioning as an "object beam". Intersectionof the reference beam and object beam, in the film, forms interferencefringes that are oriented substantially parallel to the film plane.These fringes form a reflection hologram, which functions as a mirror,when viewed with light projected on the front surface of the film. Apotential difficulty with the "on-axis" mode of operation may occur ifthe film and its support absorb a substantial portion of the beam usedto image the film, in which case the reflected object beam may be tooweak to form a satisfactory hologram. If this should occur, however, thefilm formulation is readily adjusted to minimize the problem.

It has been found to be advantageous to preheat the film, and then imagethe film while it still is at an elevated temperature. In thisembodiment the film is heated to a moderate temperature, typically inthe range of approximately 30° to 50° C., and then exposed to thecoherent light source while the film is still warm. Preheating has beenfound to improve reflection efficiency of the imaged film and toincrease photospeed. Thus, preheating permits use of a lower energylaser and/or allows the imaging step to be completed more quickly.

After the holographic mirror has been formed by either of thesetechniques, the image is fixed by flooding the film with actinicradiation. This may be achieved by exposing the film to normal roomlight, but it is preferred to flood the surface with higher intensitylight, ultraviolet light, or a combination thereof, to completepolymerization of the monomer component of the film.

The reflection holographic mirrors described above have improvedreflection efficiency compared to prior art photopolymer compositions ofHaugh. Whereas the Haugh formulations typically will have a reflectionefficiency less than 10%, reflection efficiencies in the range ofapproximately 15% to over 60% are achieved in accordance with theinvention. Surprisingly, the reflection efficiencies are even furtherimproved if the imaged film is either further treated with a particularclass of liquids that process the hologram, or is heated, as describedhereinafter. These enhancement techniques will increase the reflectionefficiency, generally two or three fold, to above 70%, and as high as99%, with no apparent detrimental effects. Concurrently, the holographicmirror can reflect light over a broader bandwidth.

LIQUID ENHANCEMENT

The class of liquids that are particularly effective in enhancingreflection holograms are organic liquids which swell the hologram, e.g.,alcohols, ketones, esters, glycol alkyl esters, etc. Use of one or moresuch enhancing agents is generally all that is required to effect imageenhancement. The enhancing agent may be a single liquid or a mixture ofsuch liquids of varying activity. Diluents, e.g., water, hydrocarbonsolvents, can be present to decrease the concentration of the enhancingagent. Diluents are "inert solvents" which, when they are appliedalonetto the hologram surface, have substantially no effect onreflection efficiency. Diluted enhancing agents are used in the instancewhen limited equilibrated enhancement is desired at lower than maximumreflectance, or when use of the enhancing agent alone causes somedissolving of the hologram. Additional treatment of such limitedequilibrated enhancement is possible with a more concentrated or moreactive enhancing agent.

Enhancing agent typically is applied after the reflection hologram hasbeen fixed by uniform actinic exposure. The reflection hologram may beimmersed in the enhancing agent or may be applied by other means. Theprocedure for applying the enhancing agent to the imaged holographicrecording medium generally is controlled to obtain a uniform enhancementof the reflection hologram and to prevent damage to the polymeric image,which is softened by the swelling action of the enhancing agent.Ideally, just sufficient enhancing agent is needed to uniformly wet theimage surface without either flooding it or applying tangential orcompressive forces. However, since the rate of enhancement of thediluted agents of this invention is slower and can be repeated,uniformity can be insured by multiple applications. Any method may beused to uniformly apply the enhancing agent to the hologram provided themethod does not entail abrasive or compressive forces which woulddistort or mar the image.

A satisfactory method of applying the enhancing agent is by lightlydrawing across the image area the edge of a paint brush or otherapplicator such as a foraminous wick, soaked in enhancing agent. If theimage area is small this procedure might be accomplished with a smallbrush or a felt-tip pen. If the image area is large, a felt-edgesqueegee of sufficient length might be used. In either case theenhancing agent is supplied uniformly from the applicator to thehologram and is absorbed into the hologram to increase its reflectionefficiency. In place of felt, any foraminous material may be used suchas paper, and woven and nonwoven fabrics. Similarly, the enhancing agentmay be applied as a mist, e.g., using an airbrush; or carefully coatedas a liquid film. Excess enhancing agent that may be present is removedfrom this hologram by known means. Normal evaporation or speededevaporation by air impingement using air at ambient temperature orelevate temperature are useful in removing excess enhancing agent. Theenhancing agent may also be removed by treating with diluentnonenhancing agent.

Enhancing agents useful in this invention include: glycol alkyl ethers,e.g., 2-methoxyethanol, 2ethoxyethanol and 2-butoxyethanol; alcohols,e.g., methanol, ethanol, butanol, 1- or 2-propanol; ketones, e.g.,acetone, methyl ethyl ketone, cyclohexanone, etc.; esters, e.g., ethylacetate, etc.; as well as other enhancing agents.

Diluents that may be present with the aforementioned enhancing agentinclude: water; inert hydrocarbon solvent, e.g., a mixture of C₈₋₁₀isoparaffins with a boiling point range of 116°-149° C., hexane;cyclohexane; heptane; 1,2-dichloroethane; trichlorotrifluoroethane; andthe like.

Typically, maximum enhancement of the entire film is desired, requiringfull strength, treatment of the film by a highly active agent.Surprisingly, the reflection efficiency remains at the equilibratedvalue even after excess agent has been removed. In those instances whereimmersion is not used or where isolated areas of the film are to beenhanced, controlled methods of application identified above may be usedto prevent flooding of the hologram surface and retain the agent in thedesired isolated area.

It has been found that liquid enhancement works best with films thathave not been Thermally Enhanced (described below). Liquid enhancementincreases refractive index modulation and shifts playback wavelength toa higher value. It also has been found that the shift in playbackwavelength achieved by liquid enhancement tends to be reversible to theextent that the liquid may subsequently evaporate from the film.Accordingly, it may be desired to select liquids that will remain in thefilm, once absorbed, or to provide an impervious cover layer over thetreated film.

THERMAL ENHANCEMENT

Reflection holograms formed using the unique films of this invention maybe thermally treated to irreversibly enhance reflection efficiency up toabout 100%. In this embodiment, a reflection holographic mirror is firstformed in the film as described above. The film is then heated to atemperature above 50° C., and preferably between 80° and 160° C., for acommensurate time period to maximize enhancement. Two to three foldimprovements in refractive index modulation are readily achieved.Thermal enhancement treatment may be carried out either before or afterthe image is fixed by flooding the film with actinic radiation asdescribed above, but typically it is carried out after the fixing step.The thermal treatment may concurrently fix the enhanced hologram bythermally hardening or polymerizing the photopolymerizable material inthe hologram. Both the rate of thermal enhancement and the rate ofthermal hardening increase with increasing temperature, with most of thebenefits being achieved during early stages. For example, when using a100° C. enhancement temperature most of the enhancement occurs duringthe first 5 to 10 minutes, with little further improvement occurringafter one hour.

In the practice of this embodiment of the invention, the reflectionhologram is heated by any conventional method. For example, the film maybe heated in a simple convection oven, irradiated with infrared ormicrowave radiation, or contact heated on a hot shoe or in a laminationpress. Whichever means is used, care is needed to prevent distortion ordamage to the photopolymer layer containing the reflection hologram.

Thermal enhancement is particularly useful in the preparation of Head-UpDisplays for use in windshields and other glass laminate structures.Since these structures are curved, it generally is more convenient toimage the film to contain the holographic mirror prior to lamination tothe glass, rather than after lamination, to simplify the optics neededto image the film. Thus, sufficient heat may be applied duringlamination to thermally enhance the holographic mirror.

After removal of the temporary support, the laminated glass sheet may beused as an Optical Combiner in a Head-Up Display. For many applications,however, the laminated glass sheet (after removal of the temporarysupport) is then placed in a lamination press along with a secondmatting glass sheet with a Butacite® polymer sheet therebetween so thatthe photopolymer film is in face to face contact with the Butacite®interleaf. Heat and pressure are applied to the glass-sandwich structure(e.g., about 130° to 150° C.) whereby the reflection hologram isenhanced and fixed concurrently with forming a glass laminate.Surprisingly, a safety glass laminate is thereby formed that contains aholographic mirror substantially free of distortion. The safety glasslaminate can be used as the Optical Combiner in a "Head-Up" Display.While glass typically is used in such displays, other transparent sheetmaterial may also be used for other applications, such as quartz,polymethyl methacrylate, polycarbonate, polystyrene, and the like,provided that the selected thermal treatment conditions do not destroythe material.

TREATMENT WITH LIQUID MONOMER

It also has been found that optical properties of the reflectionhologram, such as reflection efficiency, tend to be stabilized againstdegradation over time if the film is treated with a solution containingliquid monomer after the reflection hologram has been formed, andpreferably after thermal enhancement. In this treatment the film surfaceis exposed to the liquid monomer solution by immersion, spraying, orsimilar techniques to allow the monomer to be absorbed into the film.The monomer may be the same monomer contained in the film composition,or a different liquid monomer. The film is then dried, and the absorbedmonomer is polymerized by exposing the film to actinic radiation such asultraviolet or visible light. This treatment not only has a stabilizingeffect on the optical properties, but also affects the spacing betweeninterference fringe planes, thereby causing the holographic mirror toreflect a longer wavelength of light. Reflection efficiency also may beaffected. Thus, through the selection of particular liquid monomers,carrying solvent, and soak time before polymerization it is possible topermanently modify the optical properties of the film.

SHIFT IN WAVELENGTH OF RESPONSE

If desired, the film may contain a relatively volatile agent during theimaging step, which is subsequently removed after the imaging. In thisembodiment the fringe spacing is reduced when the agent is removed,causing the film to reflect a shorter wavelength than was used to formthe fringes. This effect can be achieved through selection of solventsor plasticizers that are compatible with the selected film composition,and which can be removed by evaporation.

EVALUATION OF CANDIDATE FILMS

To evaluate candidate films, holographic mirrors are prepared and valuesdetermined for reflection efficiency at the wavelength of maximumreflection. Refractive index modulation (M) is then calculated from thereflection efficiency and film thickness.

Film elements are prepared comprising, in order: a 0.1 mm clearpolyethylene terephthalate film support; a dried layer of the candidatephotopolymerizable film composition having a thickness of 15 to 35micrometers; and a 0.023 mm polyethylene terephthalate cover sheet. Thefilm elements are cut into uniform sections, the cover sheet is removed,and the element is hand laminated by contacting the tackyphotopolymerizable film composition directly to either a glass plate orthe glass back of an aluminum front-surface mirror. The film support istypically left in place to protect the photopolymerizable filmcomposition during exposure and handling operations.

Holographic mirrors are formed in the candidate film compositionsmounted on front-surface mirrors, using the "on-axis" techniquepreviously described, by exposure to a collimated laser beam orientedperpendicular to the film plane and reflecting back on itself.Conveniently, the laser beam is the TEM_(oo) mode of an argon laser at488 or 514 nm, or at a Krypton laser at 647 nm. Coatings mounted onglass plates are generally processed the same as those mounted on thefront-surface mirror. After exposure to record the holographic mirror,the film element is overall exposed to ultraviolet and visible light.The film element is then removed from the mirror and transmissionspectra is recorded at 400-700 nm using a conventionalspectrophotometer. If the film is laminated to a glass or plasticsubstrate, the processing and measuring steps can be performed withoutremoving the film from the substrate. The intensity of light transmittedthrough the film at the wavelength of maximum reflection (I_(trans)), ismeasured as well as the intensity of light transmitted through the filmin areas where there is no holographic Image (I_(o)). Maximum reflectionefficiency (η) is calculated from the formula: η=[1-(I_(trans) /I_(o))].Also, the intensity of reflected light is plotted versus wavelength ofthe light, and the bandwidth is measured at which 50% or more of thereflected light is reflected (i.e., bandwidth at one-half max., fwhm).The holographic mirror is then heated to 80° to 150° C. for 30 to 60minutes in a convection oven, cooled to room temperature, and analyzedagain by recording and measuring the transmission spectra.

Refractive index modulation of the holographic mirror is calculated fromthe maximum reflection efficiency (η) using Kogelnik's coupled wavetheory, which for an unslanted holographic mirror in which the incidentradiation is perpendicular to the plane of the mirror, is represented bythe formula: ##EQU1## where η=the maximum reflection efficiency;

M=refraction index modulation;

λ=probe radiation wavelength in free space; and

d =mirror (i.e., film) thickness.

Solving this equation for M, refractive index modulation is calculatedas: ##EQU2## Refractive index modulation represents the magnitude ofdifferences in refractive index within the film after it has been imagedto contain the reflection hologram. It is not thickness dependent, butdescribes the inherent capability of the film composition to record arefractive index change, i.e., reflection hologram. Films having higherrefractive index modulations will have higher reflection efficienciesand bandwidths at the same thickness.

Useful film compositions that may be selected in practicing theinvention have a refractive index modulation of at least 0.001, andgenerally will be at least 0.005 in order to achieve high reflectionefficiencies while minimizing the film thickness. Compositions having arefractive index modulation higher than 0.01 are particularly useful.With these films reflection efficiencies higher than 15%, and generallyin the order of 70% to 99%, are readily achieved at film thickness of 10to 100 micrometers that are particularly useful in the fabrication ofHead-Up Displays, notch filters, and the like. From the formula providedabove, it is readily computed that 10 and 100 micrometer films having arefractive index modulation of 0.01 will have a reflection efficiency ofapproximately 31% and 100%, respectively. In contrast, prior artphotopolymer compositions that have been proposed by Haugh forholographic applications typically will have a refractive indexmodulation of 0.001 or less, and holographic mirrors produced from thephotopolymer compositions typically have a reflection efficiency nohigher than 10 % at comparable thicknesses.

HEAD-UP DISPLAYS

The laminated glass windshield, either bearing the imaged film on itssurface or as a sandwich as described above, may be used as The OpticalCombiner in a Head-Up Display (HUD). Referring to FIG. 2, the Combiner(1) is mounted on the front windshield (2) of the vehicle in a positionsuch that displayed information (e.g., vehicle speed, gauge data, etc.)is readily available to the viewer (3). The desired information isprojected from a source, such as a CRT or vacuum fluorescent displayhaving a curved faceplate (4), through a projection lens system (5), andonto a mirror (6) that reflects the light onto the Combiner. TheCombiner, in turn, reflects the light bearing the desired information tothe viewer. Other optical systems for projecting the information ontothe Combiner will be apparent to those skilled in the art. Likewise,details of other applications for the Combiner, such as mounting on apivotal transparent screen or on the visor of a helmet, for aircraftapplications, will be apparent to those skilled in the art.

The Optical Combiner only reflects light having a narrow bandwidth thatis determined by the wavelength of coherent light that was used to imagethe film, the imaging geometry, and the subsequent processing of thefilm. Thus, the broad spectrum of light in front of the vehicle readilypasses through the windshield to the viewer, enabling the viewer to seethe path of the vehicle although the Combiner is mounted in the field ofvision.

EXAMPLES

The invention will now be further illustrated by reference to thefollowing examples, which do not limit the invention:

GENERAL PROCEDURES Sample Preparation

Coating solutions without visible sensitizer, DEAW or JAW, were preparedunder yellow or red light. After addition of DEAW or JAW, all operationson solutions and their resulting coatings were performed under red lightonly. To further protect them from actinic light, all solutions wereprepared and stored in amber bottles. Solutions were prepared by addingcomponents to the solvent and mixing with a mechanical stirrer untilthey completely dissolved. The solvent was a mixture of dichloromethane(90-95% by weight) and methanol (5%), ethanol (10%), or 2-propanol (10%)unless otherwise specified.

Solutions were coated onto a 4-mil clear film support of polyethyleneterephthalate at a speed of 4 to 8 fpm using a Talboy coater equippedwith a 6-8 mil doctor knife, 12 ft drier set at 40°-50° C., and alaminator station. A cover sheet of 1 mil polyethylene terephthalate waslaminated to the coatings after drying. Coating samples were stored inblack polyethylene bags at room temperature until used.

Sample Evaluation

Coated film was cut into 4x5-inch sections, the cover sheet was removed,and the film then mounted by hand laminating the tacky coating directlyto either the glass back of an aluminum front-surface mirror or to aglass plate. The film support was left in place during exposure andinitial handling operations.

Coatings mounted on front surface mirrors were evaluated by recordingholographic mirrors and determining their reflection efficiency,bandwidth, and wavelength of maximum reflection. The holographic mirrorswere formed by actinic exposure to a collimated laser beam, TEM_(oo)mode, oriented perpendicular to the film plane and reflecting back onitself. Unless otherwise noted, the 488 nm line of an argon-ion laserwas used. The beam had a 2.5-3.0 cm diameter and an intensity of 10-54mW/cm². Laser exposure times ranged from 5-10 seconds, corresponding to200-270 mJ/cm² total exposure. After recording holographic mirrors, filmsamples were overall exposed to ultraviolet and visible light using aDouthitt type DCOP-X exposure unit equipped with a mercury arcphotopolymer lamp (Theimer-Strahler #5027). The film support and coatingwere then removed from the front surface mirror and transmission spectraof the unprocessed holographic mirrors were recorded at 400-600 nm usinga Hitachi Perkin-Elmer model 330 spectrophotometer. Maximum reflectionefficiency, wavelength, and bandwidth at half maximum (fwhm) weredetermined from the transmission spectra. In examples 28-53 theholographic mirrors were then thermally processed by heating to 80° or150° C. for 30 minutes in a convection oven, cooled to room temperature,and analyzed again by recording and measuring their transmissionspectra.

Coatings mounted on glass plates were exposed to form holographicmirrors, as described above, except each plate was tightly clamped to afront surface aluminum mirror having the plate oriented such that thebeam, in order, passes through the glass, the coating, and the filmsupport, and then reflects back on itself. Coating samples withholographic mirrors were overall exposed using the Douthitt exposureunit described above. Where indicated, the plate was index matched usingxylene or mineral oil. Generally, the film support was then removed,leaving the coating on the glass plate. Unprocessed holographic mirrorswere analyzed by recording and measuring their transmission spectra,after which they were thermally processed by heating to 150° C. in aconvection oven, cooled to room temperature, and analyzed again. In somecases, the film support was left in place over the coating duringthermal processing and evaluation.

Coating thicknesses were measured on photocured samples by scratchingthrough the coating to the glass plate, then measuring the profile usinga Sloan DEKTAK 3030 surface profile monitoring system. For each sample,the refractive index modulation, M, of the mirror was calculated fromthe reflection efficiency at the wavelength of maximum reflection,coating thickness, and wavelength of maximum reflection usingKogelnik's, coupled wave theory, previously described. In the Examples,reflection efficiency at the wavelength of maximum reflection isreported as "Reflection Efficiency".

    ______________________________________                                        GLOSSARY OF CHEMICAL NAMES                                                    ______________________________________                                        BHT         2,6-Di-tert-butyl-4-methylphenol;                                             CAS 128-37-0                                                      Butacite ® B140C                                                                      Poly(vinylbutyral), plasticized with                                          4G7                                                               CAB 531-1   Cellulose acetate butyrate, Eastman                                           type 531-1; CAS 9004-36-8                                         DEA         Diethyladipate                                                    DEAW        Cyclopentanone, 2,5-bis{[4-                                                   (diethylamino)-phenyl]-methylene};                                            CAS 38394-53-5                                                    EBPDA       Ethoxylated bisphenol-A diacrylate;                                           CAS 24447-78-7                                                    4G7         Tetraethylene glycol diheptanoate;                                            HATCOL 5147                                                       2-HPA       2-Hydroxypropyl acrylate;                                                     propyleneglycol monoacrylate                                      MMT         4-Methyl-4H-1,2,4-triazole-3-thiol;                                           CAS 24854-43-1                                                    NVC          .sub.-- N-Vinyl carbazole; 9-Vinyl carbazole;                                CAS 1484-13-5                                                      -o-Cl-HABI 2,2'-Bis( -o-chlorophenyl)4,4',5,5'-                                          tetraphenyl-1,1'-biimidazole;                                                 CAS 1707-68-2                                                     POEA        2-Phenoxyethyl acrylate;                                                      CAS 48145-04-6                                                    PVB         Poly(vinylbutyral), Aldrich, average                                          M.W. 36,000; CAS 63148-65-2                                       TDA         Triethylene glycol diacrylate;                                                CAS 1680-21-3                                                     TDC         Triethylene glycol dicaprylate                                    TMPTA       Trimethylolpropane triacrylate;                                               2-ethyl-2-(hydroxymethyl)-1,3-                                                propanediol triacrylate;                                                      CAS 15625-89-5                                                    Vinac ® B-15                                                                          Poly(vinylacetate), Air Products,                                             M.W. 90,000; CAS 9003-20-7                                        Vinac ® B-100                                                                         Poly(vinylacetate), Air Products,                                             M.W. 500,000; CAS 9003-20-7                                       FC-430      Fluorad FC ® 430, liquid nonionic                                         surfactant; 3M Company; CAS 11114-17-3                            JAW         Cyclopentanone, 2,5-bis[(2,3,6,7-                                             tetrahydro-1H,5H-benzo[i,j]quinolizin-                                        9-yl)methylene]-                                                  PBPM         -p-Biphenyl methacrylate                                         Photomer ® 4039                                                                       Phenol ethoxylate monoacrylate; CAS                                           56641-05-5; Henkel Process Chemicals                                          Co.                                                               SR-349      Ethoxylated bisphenol A diacrylate; CAS                                       24447-78-7; Sartomer Company, West                                            Chester, PA                                                       TBPM         .sub.- t-Butylphenyl methacrylate.                               ______________________________________                                    

CONTROL EXAMPLES A-B; EXAMPLES 1-2

Control Examples A and B, with either NVC or POEA as monomer and CAB asbinder, either were inoperative or had poor reflection efficiency andspectral bandwidth. Useful coatings were achieved using poly(vinylacetate) binder.

The formulations shown below were prepared and coated with a Talboycoater equipped with a 7 mil doctor knife. All quantities are in grams,unless otherwise indicated. The film in control example A was not imagedsince it was opaque with crystals as coated. The film from Example 1also formed crystals but slowly enough to allow imaging of the film.Plates were prepared and holographic mirror imaged as described aboveexcept that the 514 nm beam of an argon ion laser was used at a power ofabout 10 mW. Film thicknesses, reflection efficiencies, and spectralbandwidths are repeated below.

    ______________________________________                                                     Example Number                                                                A     B        1        2                                        ______________________________________                                        Vinac B-15     --      --       14.16  14.25                                  CAB 531-1      14.22   14.25    --     --                                     NVC            9.04    --       9.04   --                                     POEA           --      9.06     --     9.04                                    -o-Cl-HABI    0.74    0.74     0.74   0.73                                   MMT            0.251   0.250    0.251  0.250                                  DEAW           0.012   0.012    0.012  0.012                                  BHT            0.001   0.001    0.001  0.001                                  Methanol       12.2    12.2     12.2   12.2                                   Methylene Chloride                                                                           110.3   109.9    110.1  109.8                                  Film Thickness, micron                                                                       --      17.1     16.0   18.9                                   Reflection Efficiency, %                                                                     --      3        15     27                                     Spectral Bandwidth, nm                                                                       --      5        5      7                                      Refractive Index                                                                             --      0.0017   0.0042 0.005                                  Modulation                                                                    ______________________________________                                    

The holographic mirrors were then processed in a bath composed of 3%cyclohexanone in isopropanol. The mirrors were immersed in the bath fortwo minutes, air dried for about five minutes, immersed in the developerbath for another two minutes, and air dried overnight. After drying, %transmission spectra were obtained. The bandwidth for Example 1 couldnot be measured due to the low reflection efficiency and width of thetransmission band. The film from Example B wrinkled during developmentand a reflection could not be detected. Data obtained is given below.

    ______________________________________                                                      Example Number                                                                A    B      1         2                                         ______________________________________                                        Reflection Efficiency, %                                                                      --     --     3       78                                      Spectral Bandwidth, nm                                                                        --     --     --      18                                      Refractive Index Modulation                                                                   --     --     0.0018  0.012                                   ______________________________________                                    

EXAMPLE 3

This example shows good performance using poly(vinylbutyral),particularly in compositions combining NVC and POEA liquid monomer.

    ______________________________________                                        Butacite ® B140C   179.8 g                                                POEA                   54.9 g                                                 NVC                    37.6 g                                                  -o-Cl-HABI            2.5 g                                                  MMT                    2.5 g                                                  BHT                    0.025 g                                                DEAW                   0.509 g                                                Methanol               554 g                                                  Tetrahydrofuran        554 g                                                  ______________________________________                                    

The formulation was hand coated onto 4 mil polyethylene terephthalatefilm through a 1 mil doctor knife. The film was air dried at roomtemperature before applying at 1 mil polyethylene terephthalate film ascover sheet. Plates were prepared and holographic mirrors imaged asdescribed above. Each plate was exposed for 90 seconds with the 488 nmbeam with a power of about 30 mW. The plate and mirror combination wereoriented at either normal to or 40° off normal to the incident laserbeam. Exposures made at normal to the incident beam will be referred toas "0°" and those at 40° off normal will be referred to as "40°". Thefollowing results were obtained:

    ______________________________________                                        Angle     Measured Reflection Efficiency                                      ______________________________________                                        40°                                                                              13%                                                                 40°                                                                              12%                                                                  0°                                                                              18%                                                                  0°                                                                              20%                                                                 ______________________________________                                    

EXAMPLES 4-6

A stock formulation was prepared using 75 g of Butacite® B140C, 6.25 go-Cl-HABI, 2.5 g MMT, 0.125 g DEAW, and 500 g 10% methanol/90% methylenechloride. From this stock formulation three separate film formulationswere prepared using 117 g portions for each formulation and adding toeach formulation a total of 8 g of monomer. Each formulation was coatedas described above. Film samples were mounted on glass plates andholographic mirrors prepared as in Example 3. The plate and mirrorcombination was oriented normal to the incident laser beam. Results areshown below.

    ______________________________________                                        Example                     Reflection                                        Number     Monomer(s)       Efficiency                                        ______________________________________                                        4          100% POEA        2%                                                5          100% NVC         4%                                                6          40.6% NVC, 59.4% POEA                                                                          15%                                               ______________________________________                                    

EXAMPLES 7-11

These are useful compositions similar to the poly(vinylbutyral) Examples3-6, but include a liquid plasticizer. The examples illustrate thatfavorable and also show that good results can be obtained including aliquid plasticizer.

The formulations listed below were coated as described above. Allquantities are in grams, unless otherwise indicated. Plates wereprepared as described above and holographic mirrors generated bysplitting the 488 nm beam from an Argon ion laser and impinging thecollimated coherent beams onto opposite sides of the plate with theangle between them about 180° . All films were exposed for 90 seconds.Reflection efficiencies and film thicknesses are given below.

    ______________________________________                                        Example Number                                                                7            8        9        10     11                                      ______________________________________                                        PVB     10.6     10.6     10.6   13.1   10.6                                  NVC     5.20     5.19     5.19   5.20   6.99                                  POEA    2.08     2.08     2.08   2.08   2.79                                  TDC     2.51     --       --     --     --                                    DEA     --       2.67     --     --     --                                    4G7     --       --       2.56   --     --                                     -o-Cl- 0.643    0.642    0.642  0.643  0.643                                 HABI                                                                          MMT     0.209    0.209    0.209  0.209  0.209                                 DEAW    0.011    0.011    0.011  0.011  0.011                                 BHT     0.001    0.001    0.001  0.001  0.001                                 Methanol                                                                              10.4     10.4     10.4   10.4   10.4                                  Methylene                                                                             93.5     93.4     93.4   93.5   93.5                                  Chloride                                                                      Film    20.6     20.5     20.5   19.8   19.0                                  thickness,                                                                    micron                                                                        Reflection                                                                            21       27       20     28     19                                    Efficiency,                                                                   Refractive                                                                            0.0037   0.0044   0.0036 0.0046 0.0038                                Index                                                                         Modulation                                                                    ______________________________________                                    

EXAMPLES 12 AND 13

These are useful compositions with poly(vinylacetate) binder, combinedwith a mixture of NVC and POEA monomer and TDC plasticizer. Theformulations listed below were coated and holographic mirrors imaged asdescribed in Example 7 except that exposure times for both films were 60seconds. Film thicknesses and reflection efficiencies are reportedbelow.

    ______________________________________                                                          Example Number                                                                12     13                                                   ______________________________________                                        Vinac B15           12.6     15.1                                             NVC                 6.18     2.47                                             POEA                2.55     6.1                                              TDC                 2.56     --                                                -o-Cl-HABI         0.75     0.76                                             MMT                 0.26     0.25                                             DEAW                0.012    0.012                                            BHT                 0.0013   0.0016                                           Methanol            12.3     12.3                                             Methylene Chloride  110.2    110.2                                            Film thickness, micron                                                                            18.6     18.6                                             Reflection Efficiency, %                                                                          22       22                                               Refractive Index Modulation                                                                       0.0042   0.0042                                           ______________________________________                                    

EXAMPLES 14-20

Additional useful compositions prepared from poly(vinylacetate) showingthe advantage of using NVC/POEA mixtures are shown below. The listedformulations were coated and holographic mirrors imaged as described inExample 7. Reflection efficiencies and film thicknesses are reportedbelow.

    ______________________________________                                                   Example Number                                                                  14       15       16     17                                      ______________________________________                                        Vinac B15    12.5     12.5     12.5   12.5                                    NVC          --       2.53     3.51   1.54                                    POEA         7.85     5.30     4.23   6.24                                    TDC          --       --       --     --                                       -o-Cl-HABI  0.617    0.617    0.617  0.617                                   MMT          0.029    0.029    0.029  0.0209                                  DEAW         0.010    0.010    0.010  0.010                                   BHT          0.001    0.001    0.001  0.001                                   Methanol     10.2     10.2     10.2   10.2                                    Methylene Chloride                                                                         91.5     91.4     91.4   91.4                                    Film thickness, micron                                                                     --*      15.0     13.1   12.8                                    Reflection   4        38       13     18                                      Efficiency, %                                                                 Refractive Index                                                                           --       0.0074   0.0045 0.0055                                  Modulation                                                                    ______________________________________                                                   Example Number                                                                  18          19       20                                          ______________________________________                                        Vinac B15    14.0        12.5     14.0                                        NVC          --          1.51     --                                          POEA         6.23        5.45     4.23                                        TDC          --          1.02     1.10                                         -o-Cl-HABI  0.617       0.617    0.617                                       MMT          0.209       0.209    0.209                                       DEAW         0.010       0.010    0.010                                       BHT          0.001       0.001    0.001                                       Methanol     10.2        10.2     10.2                                        Methylene Chloride                                                                         91.4        91.4     91.4                                        Film thickness, micron                                                                     14.2        15.3     13.5                                        Reflection   11          28       4                                           Efficiency, %                                                                 Refractive Index                                                                           0.0038      0.0060   0.0023                                      Modulation                                                                    ______________________________________                                         *not measured                                                            

EXAMPLES 21-23

These examples illustrate useful results can be obtained independent ofpoly(vinylacetate) molecular weight. The listed formulations were coatedand holographic mirrors imaged as in Example 7.

Reflection efficiencies and film thicknesses are reported below.

    ______________________________________                                                       Example Number                                                                21     22        23                                            ______________________________________                                        Polyvinyl Acetate,                                                                             37.4     --        --                                        Low MW, Aldrich                                                               Polyvinyl Acetate,                                                                             --       37.4      --                                        Medium MW, Aldrich                                                            Polyvinyl Acetate,                                                                             --       --        37.4                                      High MW, Aldrich                                                              NVC              7.63     7.62      7.56                                      POEA             16.0     16.0      15.9                                       -o-Cl-HABI      1.86     1.86      1.87                                      MMT              0.625    0.625     0.627                                     DEAW             0.031    0.030     0.033                                     BHT              0.004    0.003     0.003                                     Methanol         25.1     25.2      25.2                                      Methylene Chloride                                                                             241.2    227.1     226.7                                     Film thickness, micron                                                                         21.9     22.5      19.0                                      Reflection Efficiency, %                                                                       49       49        49                                        Refractive Index Modulation                                                                    0.0062   0.0060    0.0071                                    ______________________________________                                    

EXAMPLE 24

This example shows a useful poly(vinylformal) composition. Theformulation below was coated and a holographic mirror imaged asdescribed in Example 7 except that a 30 second exposure was used.

    ______________________________________                                        Polyvinyl formal    37.4                                                      NVC                 7.57                                                      POEA                15.9                                                       -o-Cl-HABI         1.87                                                      MMT                 0.626                                                     DEAW                0.030                                                     BHT                 0.003                                                     Methanol            25.1                                                      Methylene Chloride  226.1                                                     Film thickness, micron                                                                            16.7                                                      Reflection Efficiency, %                                                                          20                                                        Refractive Index Modulation                                                                       0.0045                                                    ______________________________________                                    

EXAMPLE 25

This and Examples 26 and 27 show a substantial reflection efficiencyincrease from treating the holographic mirror with a swelling solvent,whereas the prior art control composition (Example E) does not.

The formulation below was coated through a 6 mil doctor knifeapplicator. Plates were prepared and holographic mirrors imaged asdescribed in the general procedures. Film thickness and reflectionefficiency are reported below.

    ______________________________________                                        Vinac B15           37.5                                                      NVC                 7.64                                                      POEA                15.9                                                       -o-Cl-HABI         1.86                                                      MMT                 0.625                                                     DEAW                0.035                                                     BHT                 0.004                                                     Methanol            25.2                                                      Methylene Chloride  226.7                                                     Film thickness, micron                                                                            16.9                                                      Reflection Efficiency, %                                                                          44                                                        Spectral Bandwidth, nm                                                                            6                                                         Refractive Index Modulation                                                                       0.0073                                                    ______________________________________                                    

After obtaining the above data, the holographic mirror was processed bygently wiping over the mirror was processed by gently wiping over themirror a cotton swab containing acetone. After air drying for about 30minutes a % transmission spectrum was recorded. The reflectionefficiency had increased to 62% and the spectral bandwidth had increasedto 35 nm. The refractive index modulation is 0.0098.

EXAMPLE 26

The formulation shown below was coated with a 7 mil doctor knifeapplicator. Plates were prepared and holographic mirrors imaged asdescribed in the general procedures. Film thickness, reflectionefficiency and spectral bandwidth are listed below.

    ______________________________________                                        Vinac B15       37.5                                                          NVC             7.55                                                          POEA            15.9                                                          o-Cl-HABI 1.83                                                                MMT             0.623                                                         DEAW            0.017                                                         BHT             0.004                                                         Methanol        25.1                                                          Methylene Chloride                                                                            225.8                                                         Film thickness, micron                                                                        25.8                                                          Reflection Efficiency, %                                                                      48        (average 8 mirrors -                                                          all imaged                                                                    identically)                                        Spectral Bandwidth, nm                                                                        6-7       (average 8 mirrors -                                                          all imaged                                                                    identically)                                        Refractive Index Modulation                                                                   0.0051                                                        ______________________________________                                    

The holographic mirrors were then processed in a bath composed of 800 mlwater and 600 ml acetone. The mirrors were immersed in the bath for 30seconds, then water washed for 30 seconds, and then air dried. Afterdrying, % transmission spectra were obtained. Data obtained is givenbelow.

    ______________________________________                                        Maximum         77        (average 3 mirrors-                                 Reflection Efficiency, %                                                                                all imaged and                                                                processed                                                                     identically)                                        Spectral Bandwidth, nm                                                                        22-28     (average 3 mirrors                                                            all imaged and                                                                processed                                                                     identically)                                        Refractive Index                                                                              0.0082                                                        Modulation                                                                    ______________________________________                                    

EXAMPLE 27 AND CONTROL EXAMPLES C-E

The formulations below were coated through a 7 mil doctor knifeapplicator. Plates were prepared as described above and holographicmirrors imaged as described in the General Procedures. Results arereported below.

    ______________________________________                                                   Example Number                                                                27     C        D        E                                         ______________________________________                                        Vinac B15    14.2     --       14.2   --                                      CAB 531-1    --       14.2     --     14.1                                    TDA          --       --       9.04   9.04                                    NVC          2.50     2.50     --     --                                      POEA         6.49     6.50     --     --                                      o-Cl-HABI    0.73     0.73     0.74   0.74                                    MMT          0.249    0.249    0.260  0.260                                   DEAW         0.012    0.012    0.012  0.012                                   BHT          0.001    0.001    0.001  0.001                                   Methanol     12.2     12.2     12.3   12.3                                    Methylene Chloride                                                                         109.8    110.0    110.2  110.1                                   Film thickness, micron                                                                     16.9     17.7     17.0   16.4                                    Reflection Effi-                                                                           23       10       1      0                                       ciency, %                                                                     Spectral Band-                                                                             6        6        --     --                                      width, nm                                                                     Refractive Index                                                                           0.0048   0.0029   0.0009 0.0000                                  Modulation                                                                    ______________________________________                                    

The holographic mirrors were then processed in a bath composed of 3%cyclohexanone in 2-propanol. The mirrors were immersed in the bath fortwo minutes, air dried for about five minutes, immersed in the developerbath for another two minutes, and air dried overnight. After drying, %transmission spectra were obtained.

    ______________________________________                                                       Example Number                                                                27     C        D      E                                       ______________________________________                                        Reflection Efficiency, %                                                                       75       6        --   --                                    Spectral Bandwidth, nm                                                                         14       --       --   --                                    Refractive Index Modulation                                                                    0.0121   0.0022   --   --                                    ______________________________________                                    

EXAMPLES 28-31

These are useful compositions containing Vinac B-15, a low molecularweight poly(vinylacetate) binder and various crosslinking monomers.Reflection holograms recorded in these compositions can be thermallyprocessed to obtain greater reflection efficiency and bandwidth.

Four formulations were prepared, each containing a crosslinking acrylatemonomer, with or without POEA, as described below, and each containing14.2 g Vinac B-15 (56.96% by weight of total solids), 3.0 g NVC (12%),1.0 g o-Cl-HABI (4.0%), 0.50 g MMT (2.0%), 0.0075 g DEAW (0.03%), 71.25g dichloromethane, and 3.75 g methanol. The formulations were coated onpolyethylene terephthalate film, mounted on the back of a front-surfacemirror, exposed, and evaluated according to the general procedures givenabove. The reflection efficiency, bandwidth, and wavelength of maximumreflection are presented below.

    ______________________________________                                                   Example Number                                                                28     29       30       31                                        ______________________________________                                        POEA, grams  --       3.75     5.00   5.00                                    (wt %)                (15)     (20)   (20)                                    EBPDA, grams 6.25     2.50     --     --                                      (wt %)       (25)     (10)                                                    TDA, grams   --       --       1.25   --                                      (wt %)                         (5)                                            TMPTA, grams --       --       --     1.25                                    (wt %)                                (5)                                     Thickness, microns                                                                         24.8     27.4     27.2   28.0                                    Unprocessed mirrors                                                           Reflection                                                                    Efficiency, %                                                                              67.5     61.0     46.0   47.0                                    fwhm, nm     5        5        5      5                                       λmax, nm                                                                            476.5    478.5    476.5  477.0                                   Refractive Index                                                                           0.0071   0.0058   0.0046 0.0046                                  Modulation                                                                    Thermally processed: 80° C., 30 minutes,                               mirrors on polyethylene terephthalate film                                    Reflection   91       91       93     92                                      Efficiency, %                                                                 fwhm, nm     11       27       23     27                                      λmax, nm                                                                            472      466      465    467                                     Refractive Index                                                                           0.0114   0.0101   0.0109 0.0103                                  Modulation                                                                    Thermally processed: 150° C., 30 minutes,                              mirrors on polyethylene terephthalate film                                    Reflection   84.0     99.8     99.6   99.9                                    Efficiency, %                                                                 fwhm, nm     31       25       25     26                                      λmax, nm                                                                            453      447      447    449                                     Refractive Index                                                                           0.0091   0.0197   0.0181 0.0212                                  Modulation                                                                    ______________________________________                                    

EXAMPLES 32-35

These are useful compositions containing a low molecular weightpoly(vinylacetate) binder, TMPTA crosslinking monomer, and variedamounts of POEA and NVC. Reflection holograms recorded in thesecompositions can be thermally processed to obtain greater reflectionefficiency and bandwidth.

Four formulations were prepared, each containing TMPTA and POEA with orwithout NVC, as described in the following table, and each containing28.48 g Vinac B-15 (56.96% by weight of total solids), 2.0 g o-Cl-HABI(4.0%), 1.0 g MMT (2.0%), 0.015 g DEAW (0.03%). 0.005 g BHT (0.01%), 7.5g methanol, and 142.5 dichloromethane. The formulations were coated onfilm support, mounted on glass plates, exposed, and evaluated accordingto the general procedures given above. The reflection efficiency,bandwidth, and wavelength of maximum reflection are presented below.

EXAMPLE 36

This is a useful composition containing a low molecular weightpoly(vinylacetate) binder, TMPTA crosslinking monomer, and 4G7plasticizer. Reflection holograms recorded in this composition can bethermally processed to obtain greater reflection efficiency andbandwidth.

A formulation was prepared containing POEA, TMPTA, NVC, and 4G7, asdescribed below, and containing 14.24 g Vinac B-15 (56.06% by weight oftotal solids), 1.0 g o-Cl-HABI (4.0%), 0.5 g MMT (2.0%), 0.0075 g DEAW(0.03%), 0.0025 g BHT (0.01%), 3.75 g methanol, and 71.25 gdichloromethane. The formulation was coated and evaluated as in Examples32-35. The reflection efficiency, bandwidth, and wavelength of maximumreflection are presented below.

    __________________________________________________________________________                Example Number                                                                32   33   34   35   36                                            __________________________________________________________________________    TMPTA, grams (wt %)                                                                       2.5  2.5  2.5  2.5  1.25                                                      (5)  (5)  (5)  (5)  (5)                                           POEA, grams (wt %)                                                                        16.0 13.0 10.0 8.0  3.75                                                      (32) (26) (20) (16) (15)                                          NVC, grams (wt %)                                                                         --   3.0  6.0  8.0  3.0                                                            (6)  (12) (16) (12)                                          4G7, grams (wt %)                                                                         --   --   --   --   1.25                                                                          (5)                                           Thickness, microns                                                                        22.3 21.6 24.2 24.5 22.4                                          Unprocessed mirrors                                                           Reflection  32   51   64   66   58                                            Efficiency, %                                                                 fwhm, nm    6    5    5    5    6                                             λmax, nm                                                                           476  477  477  478  478                                           Refractive Index                                                                          0.0044                                                                             0.0063                                                                             0.0069                                                                             0.0070                                                                             0.0068                                        Modulation                                                                    Thermally processed: 150° C., 90 minutes,                              mirrors on glass, film support removed                                        Reflection  56   89   99.9 99.8 99.4                                          Efficiency, %                                                                 fwhm, nm    22   32   30   30   30                                            λmax, nm                                                                           464  458  447  437  437                                           Refractive Index                                                                          0.0064                                                                             0.0119                                                                             0.0244                                                                             0.0216                                                                             0.0202                                        Modulation                                                                    Thermally processed: 150° C., 90 minutes,                              mirrors between glass and film support                                        Reflection  56   80   99.9 99.2 84                                            Efficiency, %                                                                 fwhm, nm    16   25   30   42   35                                            λmax, nm                                                                           467  471  470  476  462                                           Refractive Index                                                                          0.0065                                                                             0.0100                                                                             0.0256                                                                             0.0192                                                                             0.0103                                        Modulation                                                                    __________________________________________________________________________

EXAMPLE 37

This is a useful composition containing a low molecular weightpoly(vinylacetate) binder, but no crosslinking monomer. Reflectionholograms recorded in this composition can be thermally processed,without degradation, at temperatures of about 80° C. or less, to obtaingreater reflection efficiency and bandwidth.

A formulation was prepared containing POEA and NVC, as described below,and containing 284.8 g of Vinac B-15 (56.96% by weight of total solids),20.0 g o-Cl-HABI (4.0%), 10.0 g MMT (2.0%), 0.15 g DEAW (0.03%), 0.05 gBHT (0.01%), 75 g methanol, and 1,425 g dichloromethane. The formulationwas coated and evaluated as described in Examples 28 and 32, except anextrusion-die coating bar attached to the Talboy coater was used insteadof a doctor knife. The reflection efficiency, bandwidth, and wavelengthof maximum reflection are presented below.

EXAMPLES 38-41

These are useful compositions containing a low molecular weightpoly(vinylacetate) binder and varied amounts of TMPTA crosslinkingmonomer. Reflection holograms recorded in these compositions can bethermally processed to obtain greater reflection efficiency andbandwidth.

Four formulations were prepared, each containing TMPTA, POEA, and NVC,as described below, and each containing 289.5 g Vinac B-15 (56.96% byweight of total solids), 2.0 g o-Cl-HABI (4.0%), 1.0 g MMT (2.0%), 0.015g DEAW (0.03%), 0.005 g BHT (0.01%) 7.5 g methanol, and 142.5 gdichloromethane. The formulations were coated and evaluated as describedin Example 32. The reflection efficiency bandwidth, and wavelength ofmaximum reflection are presented below.

    __________________________________________________________________________                Example Number                                                                37   38   39   40   41                                            __________________________________________________________________________    TMPTA, grams (wt %)                                                                       --   0.5  1.0  3.5  4.5                                                            (1)  (2)  (7)  (9)                                           POEA, grams (wt %)                                                                        125  12.0 11.5 9.0  8.0                                                       (25) (24) (23) (18) (16)                                          NVC, grams (wt %)                                                                         60   6.0  6.0  6.0  6.0                                                       (12) (12) (12) (12) (12)                                          Thickness, microns                                                                        26.1 20.6 27.0 26.7 23.2                                          Unprocessed mirrors                                                           Reflection Efficiency, %                                                                  57   67   72   50   53                                            fwhm, nm    5    5    5    5    5                                             λmax, nm                                                                           476  478  478  477  477                                           Refractive Index                                                                          0.0057                                                                             0.0085                                                                             0.0070                                                                             0.0050                                                                             0.0061                                        Modulation                                                                    Thermally processed: 80° C., 30 minutes,                               mirrors on film support (not determined for 38-41)                            Reflection Efficiency, %                                                                  62   --   --   --   --                                            fwhm, nm    40   --   --   --   --                                            λmax, nm                                                                           464  --   --   --   --                                            Refractive Index                                                                          0.0060                                                            modulation                                                                    Thermally processed: 150° C., 90 minutes,                              mirrors on glass, film support removed                                        Reflection Efficiency, %                                                                  0.sup.a                                                                            0.sup.a                                                                             99.9                                                                              99.4 98.7                                          fwhm, nm    --   --   33   27   22                                            λmax, nm                                                                           --   --   448  444  443                                           Refractive Index      0.0219                                                                             0.0172                                                                             0.0174                                        Modulation                                                                    Thermally processed: 150° C., 90 minutes,                              mirrors between glass and film support                                        Reflection Efficiency, %                                                                  0.sup.a                                                                            99.9 99.9 99.6 98.8                                          fwhm, nm    --   37   37   31   25                                            λmax, nm                                                                           --   469  469  472  472                                           Refractive Index                                                                          --   0.0301                                                                             0.0229                                                                             0.0194                                                                             0.0246                                        __________________________________________________________________________     .sup.a Coating hazy, hologram destroyed or very weak                     

EXAMPLES 42-43

These are examples of a low molecular weight poly(vinylacetate) basedcompositions for recording reflection holograms and use of thesecompositions to produce automobile windshield safety glass with areflection hologram internally mounted (as might be used for head-updisplays).

Two formulations were prepared, each containing Vinac B-15, TMPTA, POEA,and NVC as described below, and each containing 2.0 g o-Cl-HABI (4.0%),1.0 g MMT (2.0%), 0.015 g DEAW (0.03%), 0.005 g BHT (0.01%), 7.5 gmethanol, and 142.5 dichloromethane. The formulations were coated onpolyethylene terephthalate film support mounted on glass plates andexposed as described in the general procedures.

Unprocessed holographic mirrors on glass, film support removed, wereanalyzed by recording and measuring their transmission spectra; resultsare given below. A sheet of 30-mil Butacite® was then placed over eachholographic mirror and a second piece of glass placed on the oppositeside of the Butacite®, thus forming glass-hologram-Butacite®-glasscomposite structures which were clamped tightly together and heated to150° C. under vacuum for 60 minutes. The (safety) glass compositestructures were then removed from the vacuum oven, allowed to cool toroom temperature, and analyzed by recording and measuring theirtransmission spectra. Results are presented below.

EXAMPLE 44

This is an example of a low molecular weight poly(vinylacetate) basedcomposition containing 2-HPA, and its use to produce safety glass withan internally mounted reflection hologram.

A formulation was prepared containing Vinac B-15, TMPTA, POEA, NVC, and2-HPA, as described below, and containing 1.0 g o-Cl-HABI (4.0%), 0.5 gMMT (2.0%), 0.0075 g DEAW (0.03%), 0.0025 g BHT (0.01%), 3.75 gmethanol, and 71.25 g dichloromethane. The formulation was coated andevaluated as in Example 42. Results are presented below.

EXAMPLE 45

This is a useful composition containing Vinac B-100, a high molecularweight poly(vinylacetate) binder, and TMPTA crosslinking monomer.Reflection holograms recorded in this composition can be thermallyprocessed to obtain greater reflection efficiency and bandwidth. Thiscomposition is also useful for producing safety glass with internallymounted reflection hologram.

A formulation was prepared containing Vinac B-100, TMPTA, POEA, NVC, and2-HPA, as described below, and containing 0.75 g o-Cl-HABI (3.0%), 0.25g MMT (1.0%), 0.010 g DEAW (0.04%), 0.0025 g BHT (0.01%), 3.75 gmethanol, and 71.25 g dichloromethane. The formulation was coated andevaluated as in Example 42, except exposure was with a 514 nm argon ionlaser beam, the holographic mirror was thermally processed before makingthe safety glass composite, and a longer heating cycle was used inmaking the safety glass composite, as shown in the table below.

    ______________________________________                                                     Example Number                                                                42    43        44      45                                       ______________________________________                                        Vinac B-15     28.48   28.48     14.24 --                                     grams (wt. %)  (57)    (57)      (57)                                         Vinac B-100    --      --        --    14.73                                  grams (wt. %)                          (59)                                   TMPTA, grams (wt. %)                                                                          2.50   4.50      1.25  1.75                                                  (5)     (9)       (5)   (7)                                    POEA, grams (wt. %)                                                                          10.00   8.00      3.75  3.25                                                  (20)    (16)      (15)  (13)                                   NVC, grams (wt. %)                                                                            6.00   6.00      3.00  3.00                                                  (12)    (12)      (12)  (12)                                   2-HPA, grams (wt. %)                                                                         --      --        1.25  1.25                                                                    (5)   (5)                                    Thickness, microns                                                                           24.2    23.2      21.5  22.4                                   Unprocessed mirrors                                                           Reflection      65      57        50    32                                    Efficiency, %                                                                 fwhm, nm        4       4         4     5                                     λ.sub.max, nm                                                                         477     476       477   503                                    Refractive Index                                                                             0.0070  0.0064    0.0062                                                                              0.0046                                 Modulation                                                                    Thermally processed: 150° C., 60 minutes,                              mirrors between glass and Butacite ®                                      Reflection      84      80        85   --                                     Efficiency, %                                                                 fwhm, nm        50      33        55   --                                     λ.sub.max, nm                                                                         498     503       510   --                                     Refractive Index                                                                             0.013   0.0100    0.0121                                                                              --                                     Modulation                                                                    Thermally processed: 100° C., 30 minutes,                              then 150° C., 60 min., mirrors on glass                                Reflection     --      --        --     73                                    Efficiency, %                                                                 fwhm, nm       --      --        --     20                                    λ.sub.max, nm                                                                         --      --        --    493                                    Refractive Index                       0.0089                                 Modulation                                                                    (Processed continued) then 150° C., 90 minutes,                        mirrors between glass and Butacite ®                                      Reflection     --      --        --     72                                    Efficiency, %                                                                 fwhm, nm       --      --        --     15                                    λ.sub.max, nm                                                                         --      --        --    562                                    Refractive Index                       0.0100                                 Modulation                                                                    ______________________________________                                         Values not determined where blanks (--) are in Table                     

EXAMPLES 46-47

These are useful compositions containing high molecular weightpoly(vinylacetate) binder with and without a crosslinking monomer.Reflection holograms recorded in these compositions can be thermallyprocessed to obtain greater reflection efficiency and bandwidth.

Two formulations were prepared as listed below. The formulations werecoated as in the general procedures given above, except an extrusion-diecoating bar was used rather than a doctor knife, and the drier was setat 50°-60° C. Coatings were mounted on glass plates, exposed andevaluated according to the general procedure, except total laserexposure for each mirror was 300 mJ/cm². Results are presented below.

    ______________________________________                                                   Example Number                                                                46          47                                                     ______________________________________                                        Vinac B-100, 374.75 (59.96)                                                                              365.00 (56.96)                                     grams (wt. %)                                                                 POEA, grams (wt. %)                                                                        93.75 (15.0)  156.25 (25.0)                                      NVC, grams (wt. %)                                                                         68.75 (11.0)  75.00 (12.0)                                       TMPTA, grams 31.25 (5.0)   --                                                 (wt. %)                                                                       2-HPA, grams (wt. %)                                                                       25.00 (4.0)   --                                                 o-Cl-HABI, grams                                                                           18.75 (3.0)   25.00 (4.0)                                        (wt. %)                                                                       MMT, grams (wt. %)                                                                         12.50 (2.0)   12.50 (2.0)                                        DEAW, grams  0.188 (0.03)  0.188 (0.03)                                       (wt. %)                                                                       BHT, grams (wt. %)                                                                         0.063 (0.01)  0.063 (0.01)                                       Methanol, grams                                                                            93.8          93.8                                               Dichloromethane,                                                                           1781.2        1781.2                                             grams                                                                         Thickness, microns                                                                         14.4          17.4                                               Unprocessed mirrors                                                           Reflection    28           53                                                 Efficiency, %                                                                 fwhm, nm      5             5                                                 λ.sub.max, nm                                                                       479           479                                                Refractive Index                                                                           0.0062        0.0081                                             Modulation                                                                    Thermally processed: 100° C., 30 minutes,                              mirrors between glass and film support                                        Reflection    75           99                                                 Efficiency, %                                                                 fwhm, nm      8            13                                                 λ.sub.max, nm                                                                       479           479                                                Refractive Index                                                                           0.0139        0.0262                                             Modulation                                                                    ______________________________________                                    

EXAMPLE 48

This is a useful composition containing poly(vinylbutyral) binder andTDC plasticizer, but no crosslinking monomer. Reflection hologramsrecorded in this composition can be thermally processed, withoutdegradation, at temperatures of about 80° C. or less to obtain greaterreflection efficiency and bandwidth.

A formulation was prepared containing POEA, NVC, and TDC, as describedbelow and containing 25.4 g PVB (50.93%), 1.0 g o-Cl-HABI (2.0%), 1.0 gMMT (2.0), 0.030 g BHT (0.01%), 20.0 g 2-propanol, and 180 gdichloromethane. The formulation was coated on film support mounted onthe back of a front-surface mirror, exposed, and evaluated according tothe general procedures given above. Results are presented below.

EXAMPLES 49-51

These are useful compositions containing poly(vinylbutyral) binder andTMPTA crosslinking monomer. Reflection holograms recorded in thesecompositions can be thermally processed to obtain greater reflectionefficiency and bandwidth.

Three formulations were prepared, each containing TMPTA, POEA, and NVC,as described below, and each containing 21.6 g PVB (53.96%), 1.6 go-Cl-HABI (4.0%), 0.80 g MMT (2.0%), 0.012 g DEAW (0.03%), 0.0040 g BHT(0.01%), 16.0 g ethanol, and 144.0 dichloromethane. the formulationswere coated, exposed, and evaluated as in Example 48. Results arepresented below.

EXAMPLE 52

This is a useful composition containing poly(vinylbutyral) binder, TMPTAcrosslinking monomer, and 4G7 plasticizer. Reflection holograms recordedin this composition can be thermally processed to obtain greaterreflection efficiency and bandwidth.

A formulation was prepared containing TMPTA, POEA, NVC, and 4G7, asdescribed below and containing 17.96 g PVB (53.96), 1.33 g o-Cl-HABI(4.0%), 0.67 g MMT (2.0%), 0.010 g DEAW (0.03%), 0.0033 g BHT (0.01%),13.3 g ethanol, and 119.8 g dichloromethane. The formulation was coated,exposed, and evaluated as in Example 48. Results are presented below.

    ______________________________________                                                   Example Number                                                                48    49      50      51    52                                     ______________________________________                                        TMPTA, grams --       2.0     2.0   2.0   1.67                                (wt. %)              (5)     (5)   (5)   (5)                                  POEA, grams (wt. %)                                                                         5.0     4.0    10.0  14.0  3.3                                               (10)    (10)    (25)  (35)  (10)                                 NVC, grams (wt. %)                                                                         12.5    10.0     4.0  --    4.7                                               (25)    (25)    (10)        (15)                                 4G7, grams (wt. %)                                                                         --      --      --    --    3.3                                                                           (10)                                 Thickness, microns                                                                         24.5    23.9    26.1  24.1  26.7                                 Unprocessed mirrors                                                           Reflection    49     49       48    20   43                                   Efficiency, %                                                                 fwhm, nm      6       4       5     5     4                                   λ.sub.max, nm                                                                       474     478     476   477   477                                  Refractive Index                                                                           0.0053  0.0055  0.0050                                                                              0.0030                                                                              0.0045                               Modulation                                                                    Thermally processed: 45° C., 12 hours,                                 mirrors on film support                                                       Reflection    63     54       51    19   53                                   Efficiency, %                                                                 fwhm, nm      8       4       5     8     5                                   λ.sub.max, nm                                                                       455     476     474   472   470                                  Refractive Index                                                                           0.0064  0.0060  0.0052                                                                              0.0029                                                                              0.0052                               Modulation                                                                    Thermally processed: 45° C., 12 hours,                                 then 80° C., 30 minutes, mirrors on film support                       Reflection    77     63       55    26   63                                   Efficiency, %                                                                 fwhm, nm      27      7       7     8     5                                   λ.sub.max, nm                                                                       448     473     472   470   468                                  Refractive Index                                                                           0.0079  0.0068  0.0055                                                                              0.0035                                                                              0.0060                               Modulation                                                                    Thermally processed: 150° C., 30 minutes,                              mirrors on film support                                                       Reflection   0.sup.a 75       90    58   82                                   Efficiency, %                                                                 fwhm, nm     --      11       9     8    17                                   λ.sub.max, nm                                                                       --      424     447   457   440                                  Refractive Index                                                                           --      0.0074  0.0099                                                                              0.0060                                                                              0.0079                               Modulation                                                                    ______________________________________                                         .sup.a Coating hazy/cloudy, hologram destroyed                           

EXAMPLE 53

This is a useful composition coated on aluminized polyethyleneterephthalate film.

A formulation identical to Example 34 was prepared and coated on 4-milaluminized polyethylene terephthalate film using a 6-mil doctor knife.The drier temperature was 40°-50° C. After drying, a cover sheet ofsilicon release polyethylene terephthalate film was laminated to thecoating. A 4×5-inch section of coating was stripped of its cover sheet,mounted on a glass plate, and then exposed and evaluated according tothe general procedure described above, except a front surface mirror wasnot clamped to the plate since the aluminized polyethylene terephthalatefilm served to reflect the incident radiation. After exposure, thealuminized polyethylene terephthalate film was removed leaving theholographic mirrors mounted on glass. Results before and after thermalprocessing follow:

    ______________________________________                                                   Unprocessed                                                                            Processed: 150° C.,                                           Mirror   90 min., on glass                                         ______________________________________                                        Reflection    54        82                                                    Efficiency, %                                                                 fwhm, nm      4         30                                                    λ.sub.max, nm                                                                       477        444                                                   ______________________________________                                    

EXAMPLE 54

This example illustrates the use of JAW sensitizer.

A composition containing 16.21 gm of Vinac® B-100, 6.0 gm POEA, 1.5 gmNVC, 0.75 gm o-Cl HABI, 0.50 gm MMT, 0.025 gm FC-430, 0.0025 gm BHT,0.015 gm JAW, 6.0 gm 2-butanone, and 69.0 gm methylene chloride wascoated onto a 4-mil (0.1 mm) thick clear film support of polyethyleneterephthalate using a Talboy® coater equipped with an 8-mil doctorknife, 12 foot drier set at 40°-50° C., and a laminator station. Thecoating speed was 8 ft/minute. A cover sheet of 0.9-mil (0.02 mm)polyethylene terephthalate was laminated to the coating as it came outof the drier. Cover sheet and film support were left in place during allsubsequent handling, exposure, and processing operations.

A 4×5 inch sample of this material, sandwiched between a glass plate andan aluminized front-surface mirror, was exposed to a collimated 568 nmkrypton-ion laser beam orientated perpendicular to the film plane andpassing, in order, through the glass plate, film support, coating, andcover sheet and then, after reflecting off the mirror, back through backthe cover sheet, coating, film support, and glass plate. The beam had adiameter of about 1.4 cm and an intensity of about 15 mW/cm². Exposuretime was 20 seconds, corresponding to 300 mJ/cm² total exposure.

As described in the general procedures, the imaged sample containing theholographic mirror was overall exposed to ultraviolet and visibleradiation, heated at 100° C. for 15 minutes, and analyzed by recordingits transmission spectrum on an Hitachi Perkin-Elmer model 330spectrophotometer. The maximum reflection efficiency was 87% at 565 nm.The refractive index modulation was 0.0095.

EXAMPLE 55

This example illustrates the use of TBPM monomer.

A composition containing Vinac® B-100 (33.0 gm), Photomer® 4039 (8.5gm), TBPM (3.95 gm), SR-349 (1.5 gm), o-Cl HABI (1.85 gm), MMT (1.05gm), FC-430 (0.10 gm), and JAW (0.04 gm) in 200 gm of methylenechloride - methanol (95:5), was coated onto 2 mil (0.05 mm) polyethyleneterephthalate film using a Talboy® coater equipped with a 7-mil doctorknife, 12 foot drier set at 40°-50° C., and a laminator station. Thecoating speed was 8 ft/minutes. A cover sheet of 0.9-mil (0.02 mm)polyethylene terephthalate was laminated to the coating as it came outof the drier.

Film samples were laminated to glass plates as described in the generalprocedures and index matched with xylene to front surface mirrors.Holographic mirrors were recorded with 514 nm radiation at normalincidence as described in the general procedures. Exposure was for 40seconds with a 2.5 mW/cm² beam. Exposed samples were overall exposed asdescribed in the general procedures and heated at 100° C. for 1 hour.Reflection efficiencies were determined as described above. Thereflection efficiencies and wavelength of maximum reflection are givenin the table.

    ______________________________________                                                    Reflection       Refractive                                                   Efficiency                                                                             λ.sub.max                                                                      Index                                                        (%)      (nm)    Modulation                                       ______________________________________                                        After exposure                                                                              47         508     0.0053                                       After UV Exposure                                                                           50         508     0.0056                                       After Heating 98         508     0.0168                                       ______________________________________                                    

EXAMPLE 56

This example illustrates the use of PBPM monomer. The procedure ofExample 55 was repeated with the exception that BPPM was substituted forTBPM. The reflection efficiencies and wavelength of maximum reflectionare given in the table.

    ______________________________________                                                    Reflection       Refractive                                                   Efficiency                                                                             λ.sub.max                                                                      Index                                                        (%)      (nm)    Modulation                                       ______________________________________                                        After exposure                                                                              72         509     0.0087                                       After UV Exposure                                                                           72         507     0.0095                                       After Heating   99.9     508     0.0208                                       ______________________________________                                    

EXAMPLE 57

Examples 57 through 59 illustrates that increased reflection efficiencycan be obtained by preheating the sample.

A composition containing Vinac® B-100 (65.97%), Photomer® 4039 (15.05%),NVC (7.95%), SR-349 (5.00%), o-Cl HABI (3.69%), MMT (2.10%), FC-430(0.195%), and DEAW (0.031%) in methylene chloride - methanol (97:3), wascoated onto 4 mil (0.1 mm) polyethylene terephthalate film, dried, andcovered with a 1 mil (0.0025 mm) polyethylene terephthalate film coversheet. Coating thickness was about 1 mil (0.0025 mm). Samples werelaminated to glass plates as described in the general procedures.Exposure was as described in the general procedures, except that some ofthe laminated film samples were preheated prior to exposure.

To preheat the laminated sample, the glass plate was placed on a hotplate, whose surface temperature had been measured beforehand, with theglass in contact with the hot plate and the photopolymer layer andpolyethylene terephthalate cover sheet up. The laminated sample wasallowed to remain on the hot plate for about 60 seconds. Then it wasremoved, immediately mounted in the holder of the exposure apparatus,and exposed at 488 nm (intensity about 10 mW/cm²) for the time indicatedin the table. The control (i.e., room temperature) samples were exposedwithout being preheated on the hot plate. The pre-exposure delay time,i.e., the time between removal of a sample from the hot plate andexposure, was approximately 30 seconds. After exposure, the samples wereoverall exposed to ultraviolet and visible light, as described in thegeneral procedures, and heated at 95° C. for 15 minutes. Reflectionefficiencies were determined as described in the general procedures.

    ______________________________________                                        Hot Plate              Reflection Refractive                                  Temperature                                                                             Exposure Time.sup.a                                                                        Efficiency Index                                       (°C.)                                                                            (sec)        (%)        Modulation                                  ______________________________________                                        RT.sup.b  15           23         0.0034                                      45-50     15           33         0.0043                                      60-65     15            6         0.0016                                      75-77     15            2         0.0009                                      RT.sup.b  30           17         0.0029                                      45-50.sup.c                                                                             30           24         0.0035                                      60-65     30           17         0.0028                                      75-77     30            6         0.0016                                      ______________________________________                                         .sup.a Laser exposure time.                                                   .sup.b Room temperature  about 22° C.                                  .sup.c Preexposure delay time about 5 seconds.                           

EXAMPLE 58

Laminated film samples, prepared as described in Example 57, werepreheated on a hot plate at the temperatures indicated in the table,exposed, and analyzed as described in Example 57. The control (i.e.,room temperature) samples were exposed without being preheated on thehot plate.

    ______________________________________                                                     Reflection Efficiency (%).sup.b                                  Exposure Time (sec).sup.a                                                                    RT.sup.c  30° C.                                                                         45° C.                                ______________________________________                                         1              0        ND      24                                            5             17        27      37                                           10             26        29      27                                           15             14        ND      37                                           ______________________________________                                         ND = not determined                                                           .sup.a Laser exposure time.                                                   .sup.b Room temperature  about 22° C.                                  .sup.c Preexposure delay time about 5 seconds.                           

EXAMPLE 59

A composition containing Vinac® B-100 (65.98%), Photomer® 4039 (15.02%),NVC (7.99%), SR-349 (5.03%), o-Cl HABI (3.67%), MMT (2.08%), FC-430(0.195%), and DEAW (0.031%) in methylene chloride - methanol (97:3), wascoated onto 4 mil (0.1 mm) polyethylene terephthalate film, dried, andcovered with a 1 mil (0.0025 mm) polyethylene terephthalate film coversheet. Coating thickness was about 1 mil (0.0025 mm). Samples werelaminated to glass plates as described in the general proceduresExposure was as described in the general procedures, except that some ofthe laminated film samples were preheated prior to exposure.

Laminated film samples were preheated on a hot plate at 45° C. Prior toheating, a thin layer of mineral oil was placed on a front surfacemirror and the laminated film sample then placed on top of the mirror sothat the polyethylene terephthalate film cover sheet was in contact withthe mineral oil. This was done for both the control samples and thesamples to be heated. The samples to be heated were placed on the hotplate so that the back surface of the mirror was in contact with the hotplate. The front surface of the front surface mirror, the mineral oillayer, the polyethylene terephthalate film cover sheet, the photopolymerlayer, and the glass support, in that order, extended up from thesurface of the hot plate. The samples were heated for 120 seconds; thepre-exposure delay time was 60 seconds. The samples were exposed andanalyzed as described in Example 57. The control (i.e., roomtemperature) samples were exposed without being preheated on the hotplate.

    ______________________________________                                                       Reflection Efficiency (%).sup.b                                Exposure Time (sec).sup.a                                                                      RT.sup.c    45° C.                                    ______________________________________                                        1                20 (0.0026) 55 (0.0051)                                      3                12 (0.0019) 76 (0.0071)                                      5                48 (0.0046) 77 (0.0072)                                      10                7 (0.0014) 78 (0.0073)                                      ______________________________________                                         .sup.a Laser exposure time.                                                   .sup.b Room temperature  about 22° C.                                  .sup.c Preexposure delay time about 5 seconds.                                (Numbers in parenthesis are refractive index modulation values)          

EXAMPLE 60

A composition containing Vinac® B-100 (65.97%), Photomer® 4039 (20.05%),NVC (7.95%), o-Cl HABI (3.69%), MMT (2.10%), FC-430 (0.195%), DEAW(0.03%), and BHT (0.01%) in methylene chloride - methanol (97:3), wascoated as described in Example 57. Samples were laminated to glassplates as described in the general procedures. The glass plate mountedfilm samples were exposed at 488 nm for 10 seconds (100 mJ) to formholographic mirrors. The exposed samples were heated in an oven at 100°C. for 1 hour.

The polyethylene terephthalate cover sheet was removed and the exposedfilm samples containing the holographic mirrors immersed in a solutionof 1-propanol (80%), methanol (10%), and Photomer® 4039 (10%) for thetimes indicated in the table. The samples were removed from the solutionand the excess solution blown off. The samples were allowed to air dryfor 10 minutes, during which time they were exposed to room light, andthen a polyethylene terephthalate cover sheet was laminated to the filmsurface. The efficiencies, wavelength of maximum reflection, andbandwidth at half-maximum (fwhm) are also given in the table.

    ______________________________________                                        Immersion Reflection                                                          Time      Efficiency     λmax                                                                          fwhm                                          (sec)     (%)            (nm)   (nm)                                          ______________________________________                                         0        93             489    12                                             5        60             613    21                                            10        80             623    16                                            15        70             630    19                                            30        69             653    21                                            60        67             691    21                                            ______________________________________                                    

EXAMPLE 61

The procedure of Example 60 was followed except that the exposed filmsamples were immersed in a solution of 1-propanol (70%), methanol (15%),and Photomer® 4039 (15%) for the times indicated in the table. Thesamples were stored at room temperature and the reflection efficiencyperiodically measured. The reflection efficiencies, wavelength ofmaximum reflection, and bandwidth at half-maximum (fwhm) as a functionof storage time are also given in the table.

    ______________________________________                                        Immersion Reflection                                                          Time      Efficiency     λmax                                                                          fwhm                                          (sec)     (%)            (nm)   (nm)                                          ______________________________________                                         0        94             487    10                                             5        58             630    23                                            10        66             640    16                                            15        64             663    19                                            30        66             701    19                                            60        49             755    26                                            ______________________________________                                    

EXAMPLE 62

The procedure of Example 60 was followed except that the exposed filmsamples were immersed in a solution of distilled water (70%), 1-propanol(20%), and TDA (10%) for the times indicated in the table. Theefficiencies, wavelength of maximum reflection, and bandwidth athalf-maximum (fwhm) are also given in the table.

    ______________________________________                                        Sample Immersed in Monomer Solution for Five Seconds                          Storage   Reflection                                                          Time      Efficiency    λ.sub.max                                                                      fwhm                                          (days)    (%)           (nm)    (nm)                                          ______________________________________                                        0.sup.a   91            489     10                                            0.sup.b   67            575     30                                            8         72            573     32                                            23        66            574     33                                            214       70            571     31                                            ______________________________________                                         .sup.a Before immersion in monomer solution.                                  .sup.b After immersion in monomer solution.                              

    ______________________________________                                        Sample Immersed in Monomer Solution for Ten Seconds                           Storage   Reflection                                                          Time      Efficiency    λ.sub.max                                                                      fwhm                                          (days)    (%)           (nm)    (nm)                                          ______________________________________                                        0.sup.a   90            488     11                                            0.sup.b   61            574     34                                            8         67            572     34                                            23        62            573     33                                            214       70            568     34                                            ______________________________________                                         .sup.a Before immersion in monomer solution.                                  .sup.b After immersion in monomer solution.                              

    ______________________________________                                        Sample Immersed in Monomer Solution for Twenty Seconds                        Storage   Reflection                                                          Time      Efficiency    λ.sub.max                                                                      fwhm                                          (days)    (%)           (nm)    (nm)                                          ______________________________________                                        0.sup.a   92            488     10                                            0.sup.b   77            605     24                                            8         75            606     22                                            23        79            608     23                                            214       76            602     20                                            ______________________________________                                         .sup.a Before immersion in monomer solution.                                  .sup.b After immersion in monomer solution.                              

    ______________________________________                                        Sample Immersed in Monomer Solution for Thirty Seconds                        Storage   Reflection                                                          Time      Efficiency    λ.sub.max                                                                      fwhm                                          (days)    (%)           (nm)    (nm)                                          ______________________________________                                        0.sup.a   94            489     12                                            0         83            624     19                                            8         86            625     18                                            23        82            626     21                                            214       83            622     17                                            ______________________________________                                         .sup.a Before immersion in monomer solution.                                  .sup.b After immersion in monomer solution.                              

EXAMPLE 63

The procedure of Example 60 was followed except that the exposed filmsamples were immersed in a solution of distilled water (66.7%),1-propanol (23.8%), and TDA (9.5%) for the times indicated in the table.The efficiencies, wavelength of maximum reflection, and bandwidth athalf-maximum (fwhm) are given in the table.

    ______________________________________                                        Sample Immersed in Monomer Solution for Thirty Seconds                        Storage   Reflection                                                          Time      Efficiency    λ.sub.max                                                                      fwhm                                          (days)    (%)           (nm)    (nm)                                          ______________________________________                                        0.sup.a   92            488      9                                            0.sup.b   66            587     43                                            1         78            581     29                                            8         74            574     28                                            23        82            575     24                                            214       84            570     20                                            ______________________________________                                         .sup.a Before immersion in monomer solution.                                  .sup.b After immersion in monomer solution.                              

EXAMPLE 64

The procedure of Example 63 was followed except that two exposed sampleswhich had been exposed for the same amount of time and which had beenimmersed for the same amount of time, were laminated together. Theefficiencies, wavelength of maximum reflection, and bandwidth athalf-maximum (fwhm) for the mirrors formed by laminating together thetwo exposed film samples are given in the table.

    ______________________________________                                        Sample Immersed in Monomer Solution for Ten Seconds                           Storage   Reflection                                                          Time      Efficiency    λ.sub.max                                                                      fwhm                                          (days)    (%)           (nm)    (nm)                                          ______________________________________                                        0.sup.a   98            488      9                                            0.sup.b   66            596     72                                            1         83            571     28                                            8         82            568     26                                            23        98            565     19                                            214       98            562     16                                            ______________________________________                                         .sup.a Before immersion in monomer solution.                                  .sup.b After immersion in monomer solution.                              

    ______________________________________                                        Sample Immersed in Monomer Solution for Fifteen Seconds                       Storage   Reflection                                                          Time      Efficiency    λ.sub.max                                                                      fwhm                                          (days)    (%)           (nm)    (nm)                                          ______________________________________                                        0.sup.a   97            489     11                                            0.sup.b   68            584     50                                            1         85            582     37                                            8         82            580     34                                            23        95            580     27                                            214       94            576     24                                            ______________________________________                                         .sup.a Before immersion in monomer solution.                                  .sup.b After immersion in monomer solution.                              

Having described the invention, we now claim the following and theirequivalents:
 1. An Optical Combiner for a Head-Up Display comprising atransparent substrate that bears a transparent polymeric film containinga mirror formed by a reflection hologram, said film having a refractiveindex modulation greater than approximately 0.001 and being formed byexposing to coherent light a composition consisting essentially of:(a)approximately 25 to 90% of a polymeric binder selected from the groupconsisting of polyvinyl acetate, polyvinyl butyral, polyvinyl acetal,polyvinyl formal, interpolymers containing major segments thereof andmixtures thereof; (b) approximately 5 to 60% of an ethylenicallyunsaturated liquid monomer containing at least one phenyl, biphenyl,phenoxy, naphthyl, naphthyloxy, heteroaromatic group containing up tothree aromatic rings, chlorine or bromine moiety; (c) approximately 0 to25% of a plasticizer; and (d) approximately 0.1 to 10% of aphotoinitiator system activatable by actinic radiationwherein saidpercentages are weight percentages based on total film weight.
 2. TheCombiner of claim 1 wherein the hologram has a reflection efficiency ofat least approximately 15%.
 3. The Combiner of claim 2 wherein thetransparent substrate is selected from the group consisting of glass,quartz, polymethylmethacrylate, polycarbonate, and polystyrene.
 4. TheCombiner of claim 2 which is a lamination of, in order, a glass sheet,said transparent polymeric film containing said reflection hologram, asecond transparent polymeric film, and a second glass sheet.
 5. TheCombiner of claim 1 wherein a solid monomer is also present with saidliquid monomer and the hologram has a refractive index modulationgreater than approximately 0.005.
 6. The Combiner of claim 1 or 5wherein the ethylenically unsaturated monomer is a liquid selected fromthe group consisting of phenoxyethyl acrylate, phenol ethoxylatemonoacrylate, the di(2-acryloxyethyl) ether of bisphenol-A, ethoxylatedbisphenol-A diacrylate, 2-(1-naphthyloxy) ethyl acrylate, andortho-biphenyl methacrylate, mixtures thereof.
 7. The Combiner of claim5 wherein the ethylenically unsaturated monomer is a mixture of a solidmonomer selected from the group consisting of N-vinyl carbazole,3,6-dibromo-9-vinyl carbazole, 2,4,6-tribromophenyl acrylate ormethacrylate, pentachlorophenyl acrylate or methacrylate, 2-vinylnaphthalene, 2-naphthyl acrylate or methacrylate, 2-(2-naphthyloxy)ethylacrylate or methacrylate, para-biphenyl methacrylate, t-butylphenylmethacrylate, di-(2-acryloxyethyl)ether of tetrabromo-bisphenol-A andmixtures thereof; and a liquid monomer selected from the groupconsisting of phenoxyethyl acrylate, phenol ethoxylate acrylate, thedi(2-acryloxyethyl ether) of bisphenol-A, ortho-biphenyl methacrylate,ethoxylated bisphenol-A diacrylate, 2-(1-naphthyloxy)ethyl acrylate, andmixtures thereof.
 8. The Combiner of claim 1 or 5 containing aplasticizer selected from the group consisting oftris(2-ethylhexyl)phosphate, glyceryl tributyrate, and a compound havingthe general formula: ##STR2## wherein R₁ and R₂ each is an alkyl groupof 1 to 10 carbon atoms, R₃ is H or an alkyl group of 8 to 16 carbonatoms, R₄ is H or CH₃, x is 1-4, y is 2-20, and z is 1-20.
 9. TheCombiner of claim 8 wherein the plasticizer is selected from the groupconsisting of triethylene glycol dicaprylate, triethylene glycolbis(2-ethylhexanoate), diethyl adipate, dibutyl adipate, tetraethyleneglycol diheptanoate, dibutyl suberate, diethyl sebacate,tris(2-ethylhexyl)phosphate, and glyceryl tributyrate.
 10. The Combinerof claim 5 wherein the components in said film are present in thefollowing approximate weight ranges: binder, 45 to 75%; monomer, 15 to50%; and plasticizer, 0 to 15%.
 11. The Combiner of claim 10 wherein thehologram has a refractive index modulation greater than approximately0.010.
 12. The Combiner of claim 5 wherein the transparent substrate isselected from the group consisting of glass, quartz,polymethylmethacrylate, polycarbonate, and polystyrene.
 13. The Combinerof claim 5 which is a lamination of, in order, a glass sheet, saidtransparent polymeric film containing said hologram, a secondtransparent polymeric film, and a second glass sheet.
 14. The Combinerof claim 5 wherein the mirror hologram has a refractive index modulationgreater than approximately 0.010.
 15. The Combiner of claim 5 whereinthe film has a thickness in the range of approximately 1 to 100micrometers.
 16. A method of forming an Optical Combiner for a Head-UpDisplay consisting essentially of:(a) mounting a transparent supportonto one side of a transparent polymeric film consisting essentiallyof:(1) approximately 25 to 90% of a polymeric binder selected from thegroup consisting of polyvinyl acetate, polyvinyl butyral, polyvinylacetal, polyvinyl formal, interpolymers containing major segmentsthereof, and mixtures thereof; (2) approximately 5 to 60% of anethylenically unsaturated liquid monomer containing at least one phenyl,biphenyl, phenoxy, naphthyl, naphthyloxy, heteroaromatic groupcontaining up to three aromatic rings, chlorine or bromine moiety; (3)approximately 0 to 25% of a plasticizer; and (4) approximately 0.1 to10% of a photoinitiator system activatable by the actinic radiation,wherein said percentages are weight percentages based on total filmweight; (b) exposing the mounted film to coherent light in a manner thatforms a reflection hologram in said film; and (c) laminating the imagedfilm to a permanent transparent substrate,said Combiner having an imagedfilm that has a refractive index modulation of at least 0.001.
 17. Theprocess of claim 16 wherein the mounted film is exposed to an objectbeam and a reference beam of coherent light that enter the transparentfilm from opposite sides to create interference fringes forming aholographic mirror.
 18. The process of claim 16 wherein the interferencefringes are substantially coplanar with the film plane.
 19. The processof claim 16 wherein the plane of the interference fringes are at anacute angle with the film plane.
 20. The process of claim 16 includingthe step of removing the transparent support after the imaged film islaminated to the permanent transparent substrate.
 21. The process ofclaim 16 wherein the polymeric film also contains a solid monomer withsaid liquid monomer and, after exposure to form a reflection hologram,has a refractive index modulation greater than approximately 0.005. 22.The process of claim 16 or 21 wherein the mounted film of step (a) isheated to approximately 30° to 50° C. immediately prior to being exposedto coherent light during step (b).
 23. The process of claim 16 or 21wherein, after step (b), the imaged film is treated with an organicliquid to increase reflection efficiency.
 24. The process of claim 23wherein the organic liquid is selected from the group consisting ofglycol alkyl ethers, alcohols, ketones, and esters.
 25. The process ofclaim 16 or 21 wherein, after step (b), the imaged film is heated to atemperature above 50° C. for a sufficient time to enhance reflectionefficiency.
 26. The process of claim 25 wherein the imaged film isheated to a temperature in the range of approximately 80° to 160° C. 27.The process of claim 25 or 26 wherein said heating occurs during step(c) lamination.
 28. The process of claim 27 wherein the resultingCombiner has a refractive index modulation of at least 0.005.
 29. Theprocess of claim 16 or 21 wherein, after step (b), the imaged film istreated with liquid monomer solution that stabilizes reflectionefficiency, said treatment comprising exposing the imaged film surfaceto liquid monomer that is absorbed by the film, drying the film, andpolymerizing the absorbed monomer by exposure to actinic radiation. 30.The process of claim 29 wherein said treatment with liquid monomer isperformed after the film is heated to a temperature above 50° C. for asufficient time to enhance reflection efficiency.